Time and Work | Mathematics (Maths) Class 8 PDF Download

 Page 1


Q u e s t i o n : 1
Rakesh can do a piece of work in 20 days. How much work can he do in 4 days?
S o l u t i o n :
It is given that Rakesh can do a piece of work in 20 days. ? Rakesh's 1 day's work =
1
20
? Rakesh's work for 4 days =
4
20
=
1
5
Thus, he can do 
1
5
th of the work in 4 days.
Q u e s t i o n : 2
Rohan can paint 
1
3
of a painting in 6 days. How many days will he take to complete the painting?
S o l u t i o n :
Rohan can paint 
1
3
rd of a painting in 6 days. ? Time taken by Rohan to complete the painting = (6 ×3) days = 18 days.
Q u e s t i o n : 3
Anil can do a piece of work in 5 days and Ankur in 4 days. How long will they take to do the same work, if they work together?
S o l u t i o n :
Time taken by Anil to do the work = 5 daysTime taken by Ankur to do the work = 4 days ? Work done by Anil in 1 day =
1
5
Work done by Ankur in 1 day =
1
4
? Work done by Anil and Ankur
Q u e s t i o n : 4
Mohan takes 9 hours to mow a large lawn. He and Sohan together can mow it in 4 hours. How long will Sohan take to mow the lawn if he works alone?
S o l u t i o n :
Time taken by Mohan to do the work = 9 hoursTime taken by Mohan and Sohan to do the work = 4 hours ? Work done by Mohan =
1
9
Work done by Mohan and Sohan =
1
4
? Work done by 
Q u e s t i o n : 5
Sita can finish typing a 100 page document in 9 hours. Mita in 6 hours and Rita in 12 hours. How long will they take to type a 100 page document if they work together?
S o l u t i o n :
Time taken by Sita to do the work = 9 hoursTime taken by Mita to do the work = 6 hoursTime taken by Rita to do the work = 12 hoursNow, Work done by Sita =
1
9
Work done by Mita =
1
6
Work
Q u e s t i o n : 6
A, B and C working together can do a piece of work in 8 hours. A alone can do it in 20 hours and B alone can do it in 24 hours. In how many hours will C alone do the same work?
S o l u t i o n :
Time taken by A to do the work = 20 hoursTime taken by B to do the work = 24 hoursTime taken by (A +B +C) to do the work = 8 hoursNow, Work done by A =
1
20
Work done by B =
1
24
Work 
Q u e s t i o n : 7
A and B can do a piece of work in 18 days; B and C in 24 days and A and C in 36 days. In what time can they do it, all working together?
S o l u t i o n :
Time taken by (A +B) to do the work = 18 daysTime taken by (B +C) to do the work = 24 daysTime taken by (A +C) to do the work = 36 daysNow, Work done by (A +B) =
1
18
Work done by (B
Q u e s t i o n : 8
A and B can do a piece of work in 12 days; B and C in 15 days; C and A in 20 days. How much time will A alone take to finish the work?
S o l u t i o n :
Time taken by (A +B) to do the work = 12 daysTime taken by (B +C) to do the work = 15 daysTime taken by (A +C) to do the work = 20 daysNow, Work done by (A +B) =
1
12
Work done by (B
Q u e s t i o n : 9
A, B and C can reap a field in 15
3
4
days; B, C and D in 14 days; C, D and A in 18 days; D, A and B in 21 days. In what time can A, B, C and D together reap it?
S o l u t i o n :
Time taken by (A +B +C) to do the work = 15
3
4
 days =
63
4
daysTime taken by (B +C +D) to do the work = 14 daysTime taken by (C +D +A) to do the work = 18 daysTime taken by (D +A +B) to
Q u e s t i o n : 1 0
A and B can polish the floors of a building in 10 days. A alone can do 
1
4
th of it in 12 days. In how many days can B alone polish the floor?
S o l u t i o n :
It is given that A and B can polish the floors of the building in 10 days. ? Work done by (A +B) in 1 day =
1
10
Now, A alone can do 
1
4
th of the work in 12 days. ? Time taken by A alone to do
Q u e s t i o n : 1 1
A and B can finish a work in 20 days. A alone can do 
1
5
th of the work in 12 days. In how many days can B alone do it?
S o l u t i o n :
It is given that A and B can finish the work in 20 days. ? Work done by (A +B) in 1 day =
1
20
Now, A alone can do 
1
5
th of the work in 12 days. ? Time taken by A alone to complete the work
Q u e s t i o n : 1 2
A and B can do a piece of work in 20 days and B in 15 days. They work together for 2 days and then A goes away. In how many days will B finish the remaining work?
S o l u t i o n :
It is given that A can finish the work in 20 days and B can finish the same work in 15 days. ? Work done by A in 1 day =
1
20
Work done by B in 1 day =
1
15
? Work done by (A +B) in 1 day
Page 2


Q u e s t i o n : 1
Rakesh can do a piece of work in 20 days. How much work can he do in 4 days?
S o l u t i o n :
It is given that Rakesh can do a piece of work in 20 days. ? Rakesh's 1 day's work =
1
20
? Rakesh's work for 4 days =
4
20
=
1
5
Thus, he can do 
1
5
th of the work in 4 days.
Q u e s t i o n : 2
Rohan can paint 
1
3
of a painting in 6 days. How many days will he take to complete the painting?
S o l u t i o n :
Rohan can paint 
1
3
rd of a painting in 6 days. ? Time taken by Rohan to complete the painting = (6 ×3) days = 18 days.
Q u e s t i o n : 3
Anil can do a piece of work in 5 days and Ankur in 4 days. How long will they take to do the same work, if they work together?
S o l u t i o n :
Time taken by Anil to do the work = 5 daysTime taken by Ankur to do the work = 4 days ? Work done by Anil in 1 day =
1
5
Work done by Ankur in 1 day =
1
4
? Work done by Anil and Ankur
Q u e s t i o n : 4
Mohan takes 9 hours to mow a large lawn. He and Sohan together can mow it in 4 hours. How long will Sohan take to mow the lawn if he works alone?
S o l u t i o n :
Time taken by Mohan to do the work = 9 hoursTime taken by Mohan and Sohan to do the work = 4 hours ? Work done by Mohan =
1
9
Work done by Mohan and Sohan =
1
4
? Work done by 
Q u e s t i o n : 5
Sita can finish typing a 100 page document in 9 hours. Mita in 6 hours and Rita in 12 hours. How long will they take to type a 100 page document if they work together?
S o l u t i o n :
Time taken by Sita to do the work = 9 hoursTime taken by Mita to do the work = 6 hoursTime taken by Rita to do the work = 12 hoursNow, Work done by Sita =
1
9
Work done by Mita =
1
6
Work
Q u e s t i o n : 6
A, B and C working together can do a piece of work in 8 hours. A alone can do it in 20 hours and B alone can do it in 24 hours. In how many hours will C alone do the same work?
S o l u t i o n :
Time taken by A to do the work = 20 hoursTime taken by B to do the work = 24 hoursTime taken by (A +B +C) to do the work = 8 hoursNow, Work done by A =
1
20
Work done by B =
1
24
Work 
Q u e s t i o n : 7
A and B can do a piece of work in 18 days; B and C in 24 days and A and C in 36 days. In what time can they do it, all working together?
S o l u t i o n :
Time taken by (A +B) to do the work = 18 daysTime taken by (B +C) to do the work = 24 daysTime taken by (A +C) to do the work = 36 daysNow, Work done by (A +B) =
1
18
Work done by (B
Q u e s t i o n : 8
A and B can do a piece of work in 12 days; B and C in 15 days; C and A in 20 days. How much time will A alone take to finish the work?
S o l u t i o n :
Time taken by (A +B) to do the work = 12 daysTime taken by (B +C) to do the work = 15 daysTime taken by (A +C) to do the work = 20 daysNow, Work done by (A +B) =
1
12
Work done by (B
Q u e s t i o n : 9
A, B and C can reap a field in 15
3
4
days; B, C and D in 14 days; C, D and A in 18 days; D, A and B in 21 days. In what time can A, B, C and D together reap it?
S o l u t i o n :
Time taken by (A +B +C) to do the work = 15
3
4
 days =
63
4
daysTime taken by (B +C +D) to do the work = 14 daysTime taken by (C +D +A) to do the work = 18 daysTime taken by (D +A +B) to
Q u e s t i o n : 1 0
A and B can polish the floors of a building in 10 days. A alone can do 
1
4
th of it in 12 days. In how many days can B alone polish the floor?
S o l u t i o n :
It is given that A and B can polish the floors of the building in 10 days. ? Work done by (A +B) in 1 day =
1
10
Now, A alone can do 
1
4
th of the work in 12 days. ? Time taken by A alone to do
Q u e s t i o n : 1 1
A and B can finish a work in 20 days. A alone can do 
1
5
th of the work in 12 days. In how many days can B alone do it?
S o l u t i o n :
It is given that A and B can finish the work in 20 days. ? Work done by (A +B) in 1 day =
1
20
Now, A alone can do 
1
5
th of the work in 12 days. ? Time taken by A alone to complete the work
Q u e s t i o n : 1 2
A and B can do a piece of work in 20 days and B in 15 days. They work together for 2 days and then A goes away. In how many days will B finish the remaining work?
S o l u t i o n :
It is given that A can finish the work in 20 days and B can finish the same work in 15 days. ? Work done by A in 1 day =
1
20
Work done by B in 1 day =
1
15
? Work done by (A +B) in 1 day
Q u e s t i o n : 1 3
A can do a piece of work in 40 days and B in 45 days. They work together for 10 days and then B goes away. In how many days will A finish the remaining work?
S o l u t i o n :
It is given that A can finish the work in 40 days and B can finish the same work in 45 days. ? Work done by A in 1 day =
1
40
Work done by B in 1 day =
1
45
? Work done by (A +B) in 1 day
Q u e s t i o n : 1 4
Aasheesh can paint his doll in 20 minutes and his sister Chinki can do so in 25 minutes. They paint the doll together for five minutes. At this juncture they have a quarrel and Chinki
withdraws from painting. In how many minutes will Aasheesh finish the painting of the remaining doll?
S o l u t i o n :
Aasheesh can paint a doll in 20 minutes, and Chinki can do the same in 25 minutes. ? Work done by Aasheesh in 1 minute =
1
20
? Work done by Chinki in 1 minute =
1
25
? Work done by
Q u e s t i o n : 1 5
A and B can do a piece of work in 6 days and 4 days respectively. A started the work; worked at it for 2 days and then was joined by B. Find the total time taken to complete the work.
S o l u t i o n :
A can do a work in 6 days, and B can do the same work in 4 days. ? Work done by A in 2 days =
2
6
=
1
3
Remaining work = 1 -
1
3
=
2
3
? Work done by (A +B)in 1 day =
1
6
+
1
4
=
2+3
12
=
5
12
? 
5
12
th
Q u e s t i o n : 1 6
6 men can complete the electric fitting in a building in 7 days. How many days will it take if 21 men do the job?
S o l u t i o n :
It is given that 6 men can complete a job in 7 days. ? Time taken by 1 man to complete the same job = (6 ×7) = 42 days ? Time taken by 21 men to complete the same job =
42
21
= 2 days
Q u e s t i o n : 1 7
8 men can do a piece of work in 9 days. In how many days will 6 men do it?
S o l u t i o n :
It is given that 8 men can complete a job in 9 days. ? Time taken by 1 man to complete the same job = (8 ×9) = 72 days ? Time taken by 6 men to complete the same job =
72
6
= 12 days
Q u e s t i o n : 1 8
Reema weaves 35 baskets in 25 days. In how many days will she weave 55 baskets?
S o l u t i o n :
It is given that Reema weaves 35 baskets in 25 days. ? Time taken by her to weave 1 basket =
25
35
day ? Time taken by her to weave 55 baskets =
25
35
×55 days =
1375
35
 days =
275
7
 days
Q u e s t i o n : 1 9
Neha types 75 pages in 14 hours. How many pages will she type in 20 hours?
S o l u t i o n :
It is given that Neha types 75 pages in 14 hours. ? Number of pages typed by her in 1 hour =
75
14
? Number of pages typed by her in 20 hours = 
75
14
×20 pages =
1500
14
 pages =
750
7
 pages
Q u e s t i o n : 2 0
If 12 boys earn Rs 840 in 7 days, what will 15 boys earn in 6 days?
S o l u t i o n :
Earnings of 12 boys in 7 days = Rs. 840 ? Earnings of 12 boys in 1 day = Rs. 
840
7
= Rs. 120 ? Earnings of 1 boy in 1 day = Rs.
120
12
= Rs. 10 ? Earnings of 1 boy in 6 days = Rs. (10 ×6)
Q u e s t i o n : 2 1
If 25 men earn Rs 1000 in 10 days, how much will 15 men earn in 15 days?
S o l u t i o n :
Earnings of 25 men in 10 days = Rs. 1000 ? Earnings of 25 men in 1 day = Rs.
1000
10
= Rs. 100 ? Earning of 1 man in 1 day = Rs.
100
25
= Rs. 4 ? Earnings of 1 men in 15 days = Rs. (15 ×4) =
Q u e s t i o n : 2 2
Working 8 hours a day, Ashu can copy a book in 18 days. How many hours a day should he work so as to finish the work in 12 days?
S o l u t i o n :
If Ashu works for 8 hours daily, he can finish the work in 18 days. If he works for 1 hour daily, he can finish the work in (18 ×8) days or 144 days. ? Number of hours he should work daily
Q u e s t i o n : 2 3
If 9 girls can prepare 135 garlands in 3 hours, how many girls are needed to prepare 270 garlands in 1 hour?
S o l u t i o n :
Number of garlands made by 9 girls in 1 hour =
135
3
= 45Number of garlands made by 1 girl in 1 hour =
45
9
= 5 ? Number of girls required to make 270 garlands in 1 hour =
270
5
= 54.
Q u e s t i o n : 2 4
A cistern can be filled by one tap in 8 hours, and by another in 4 hours. How long will it take to fill the cistern if both taps are opened together?
S o l u t i o n :
Time taken by the first tap to fill the cistern = 8 hoursTime taken by the second tap to fill the cistern = 4 hours ? Work done by the first tap in 1 hour =
1
8
Work done by the second tap in 1 hour
Q u e s t i o n : 2 5
Two taps A and B can fill an overhead tank in 10 hours and 15 hours respectively. Both the taps are opened for 4 hours and they B is turned off. How much time will A take to fill the
remaining tank?
S o l u t i o n :
( )
( )
( )
Page 3


Q u e s t i o n : 1
Rakesh can do a piece of work in 20 days. How much work can he do in 4 days?
S o l u t i o n :
It is given that Rakesh can do a piece of work in 20 days. ? Rakesh's 1 day's work =
1
20
? Rakesh's work for 4 days =
4
20
=
1
5
Thus, he can do 
1
5
th of the work in 4 days.
Q u e s t i o n : 2
Rohan can paint 
1
3
of a painting in 6 days. How many days will he take to complete the painting?
S o l u t i o n :
Rohan can paint 
1
3
rd of a painting in 6 days. ? Time taken by Rohan to complete the painting = (6 ×3) days = 18 days.
Q u e s t i o n : 3
Anil can do a piece of work in 5 days and Ankur in 4 days. How long will they take to do the same work, if they work together?
S o l u t i o n :
Time taken by Anil to do the work = 5 daysTime taken by Ankur to do the work = 4 days ? Work done by Anil in 1 day =
1
5
Work done by Ankur in 1 day =
1
4
? Work done by Anil and Ankur
Q u e s t i o n : 4
Mohan takes 9 hours to mow a large lawn. He and Sohan together can mow it in 4 hours. How long will Sohan take to mow the lawn if he works alone?
S o l u t i o n :
Time taken by Mohan to do the work = 9 hoursTime taken by Mohan and Sohan to do the work = 4 hours ? Work done by Mohan =
1
9
Work done by Mohan and Sohan =
1
4
? Work done by 
Q u e s t i o n : 5
Sita can finish typing a 100 page document in 9 hours. Mita in 6 hours and Rita in 12 hours. How long will they take to type a 100 page document if they work together?
S o l u t i o n :
Time taken by Sita to do the work = 9 hoursTime taken by Mita to do the work = 6 hoursTime taken by Rita to do the work = 12 hoursNow, Work done by Sita =
1
9
Work done by Mita =
1
6
Work
Q u e s t i o n : 6
A, B and C working together can do a piece of work in 8 hours. A alone can do it in 20 hours and B alone can do it in 24 hours. In how many hours will C alone do the same work?
S o l u t i o n :
Time taken by A to do the work = 20 hoursTime taken by B to do the work = 24 hoursTime taken by (A +B +C) to do the work = 8 hoursNow, Work done by A =
1
20
Work done by B =
1
24
Work 
Q u e s t i o n : 7
A and B can do a piece of work in 18 days; B and C in 24 days and A and C in 36 days. In what time can they do it, all working together?
S o l u t i o n :
Time taken by (A +B) to do the work = 18 daysTime taken by (B +C) to do the work = 24 daysTime taken by (A +C) to do the work = 36 daysNow, Work done by (A +B) =
1
18
Work done by (B
Q u e s t i o n : 8
A and B can do a piece of work in 12 days; B and C in 15 days; C and A in 20 days. How much time will A alone take to finish the work?
S o l u t i o n :
Time taken by (A +B) to do the work = 12 daysTime taken by (B +C) to do the work = 15 daysTime taken by (A +C) to do the work = 20 daysNow, Work done by (A +B) =
1
12
Work done by (B
Q u e s t i o n : 9
A, B and C can reap a field in 15
3
4
days; B, C and D in 14 days; C, D and A in 18 days; D, A and B in 21 days. In what time can A, B, C and D together reap it?
S o l u t i o n :
Time taken by (A +B +C) to do the work = 15
3
4
 days =
63
4
daysTime taken by (B +C +D) to do the work = 14 daysTime taken by (C +D +A) to do the work = 18 daysTime taken by (D +A +B) to
Q u e s t i o n : 1 0
A and B can polish the floors of a building in 10 days. A alone can do 
1
4
th of it in 12 days. In how many days can B alone polish the floor?
S o l u t i o n :
It is given that A and B can polish the floors of the building in 10 days. ? Work done by (A +B) in 1 day =
1
10
Now, A alone can do 
1
4
th of the work in 12 days. ? Time taken by A alone to do
Q u e s t i o n : 1 1
A and B can finish a work in 20 days. A alone can do 
1
5
th of the work in 12 days. In how many days can B alone do it?
S o l u t i o n :
It is given that A and B can finish the work in 20 days. ? Work done by (A +B) in 1 day =
1
20
Now, A alone can do 
1
5
th of the work in 12 days. ? Time taken by A alone to complete the work
Q u e s t i o n : 1 2
A and B can do a piece of work in 20 days and B in 15 days. They work together for 2 days and then A goes away. In how many days will B finish the remaining work?
S o l u t i o n :
It is given that A can finish the work in 20 days and B can finish the same work in 15 days. ? Work done by A in 1 day =
1
20
Work done by B in 1 day =
1
15
? Work done by (A +B) in 1 day
Q u e s t i o n : 1 3
A can do a piece of work in 40 days and B in 45 days. They work together for 10 days and then B goes away. In how many days will A finish the remaining work?
S o l u t i o n :
It is given that A can finish the work in 40 days and B can finish the same work in 45 days. ? Work done by A in 1 day =
1
40
Work done by B in 1 day =
1
45
? Work done by (A +B) in 1 day
Q u e s t i o n : 1 4
Aasheesh can paint his doll in 20 minutes and his sister Chinki can do so in 25 minutes. They paint the doll together for five minutes. At this juncture they have a quarrel and Chinki
withdraws from painting. In how many minutes will Aasheesh finish the painting of the remaining doll?
S o l u t i o n :
Aasheesh can paint a doll in 20 minutes, and Chinki can do the same in 25 minutes. ? Work done by Aasheesh in 1 minute =
1
20
? Work done by Chinki in 1 minute =
1
25
? Work done by
Q u e s t i o n : 1 5
A and B can do a piece of work in 6 days and 4 days respectively. A started the work; worked at it for 2 days and then was joined by B. Find the total time taken to complete the work.
S o l u t i o n :
A can do a work in 6 days, and B can do the same work in 4 days. ? Work done by A in 2 days =
2
6
=
1
3
Remaining work = 1 -
1
3
=
2
3
? Work done by (A +B)in 1 day =
1
6
+
1
4
=
2+3
12
=
5
12
? 
5
12
th
Q u e s t i o n : 1 6
6 men can complete the electric fitting in a building in 7 days. How many days will it take if 21 men do the job?
S o l u t i o n :
It is given that 6 men can complete a job in 7 days. ? Time taken by 1 man to complete the same job = (6 ×7) = 42 days ? Time taken by 21 men to complete the same job =
42
21
= 2 days
Q u e s t i o n : 1 7
8 men can do a piece of work in 9 days. In how many days will 6 men do it?
S o l u t i o n :
It is given that 8 men can complete a job in 9 days. ? Time taken by 1 man to complete the same job = (8 ×9) = 72 days ? Time taken by 6 men to complete the same job =
72
6
= 12 days
Q u e s t i o n : 1 8
Reema weaves 35 baskets in 25 days. In how many days will she weave 55 baskets?
S o l u t i o n :
It is given that Reema weaves 35 baskets in 25 days. ? Time taken by her to weave 1 basket =
25
35
day ? Time taken by her to weave 55 baskets =
25
35
×55 days =
1375
35
 days =
275
7
 days
Q u e s t i o n : 1 9
Neha types 75 pages in 14 hours. How many pages will she type in 20 hours?
S o l u t i o n :
It is given that Neha types 75 pages in 14 hours. ? Number of pages typed by her in 1 hour =
75
14
? Number of pages typed by her in 20 hours = 
75
14
×20 pages =
1500
14
 pages =
750
7
 pages
Q u e s t i o n : 2 0
If 12 boys earn Rs 840 in 7 days, what will 15 boys earn in 6 days?
S o l u t i o n :
Earnings of 12 boys in 7 days = Rs. 840 ? Earnings of 12 boys in 1 day = Rs. 
840
7
= Rs. 120 ? Earnings of 1 boy in 1 day = Rs.
120
12
= Rs. 10 ? Earnings of 1 boy in 6 days = Rs. (10 ×6)
Q u e s t i o n : 2 1
If 25 men earn Rs 1000 in 10 days, how much will 15 men earn in 15 days?
S o l u t i o n :
Earnings of 25 men in 10 days = Rs. 1000 ? Earnings of 25 men in 1 day = Rs.
1000
10
= Rs. 100 ? Earning of 1 man in 1 day = Rs.
100
25
= Rs. 4 ? Earnings of 1 men in 15 days = Rs. (15 ×4) =
Q u e s t i o n : 2 2
Working 8 hours a day, Ashu can copy a book in 18 days. How many hours a day should he work so as to finish the work in 12 days?
S o l u t i o n :
If Ashu works for 8 hours daily, he can finish the work in 18 days. If he works for 1 hour daily, he can finish the work in (18 ×8) days or 144 days. ? Number of hours he should work daily
Q u e s t i o n : 2 3
If 9 girls can prepare 135 garlands in 3 hours, how many girls are needed to prepare 270 garlands in 1 hour?
S o l u t i o n :
Number of garlands made by 9 girls in 1 hour =
135
3
= 45Number of garlands made by 1 girl in 1 hour =
45
9
= 5 ? Number of girls required to make 270 garlands in 1 hour =
270
5
= 54.
Q u e s t i o n : 2 4
A cistern can be filled by one tap in 8 hours, and by another in 4 hours. How long will it take to fill the cistern if both taps are opened together?
S o l u t i o n :
Time taken by the first tap to fill the cistern = 8 hoursTime taken by the second tap to fill the cistern = 4 hours ? Work done by the first tap in 1 hour =
1
8
Work done by the second tap in 1 hour
Q u e s t i o n : 2 5
Two taps A and B can fill an overhead tank in 10 hours and 15 hours respectively. Both the taps are opened for 4 hours and they B is turned off. How much time will A take to fill the
remaining tank?
S o l u t i o n :
( )
( )
( )
Pipe A can fill the tank in 10 hours, and pipe B can fill the tank in 15 hours. ? In 1 hour, A can fill 
1
10
th part of the tank. In 1 hour, B can fill 
1
15
th part of the tank. ? In 1 hour, A and B can 
Q u e s t i o n : 2 6
A pipe can fill a cistern in 10 hours. Due to a leak in the bottom it is filled in 12 hours. When the cistern is full, in how much time will it be emptied by the leak?
S o l u t i o n :
When there is no leakage, the pipe can fill the cistern in 10 hours. Thus, the pipe can fill 
1
10
th part of the cistern in 1 hour. When there is leakage, the pipe can fill the cistern in 12 hours. Therefore
Q u e s t i o n : 2 7
A cistern has two inlets A and B which can fill it in 12 hours and 15 hours respectively. An outlet can empty the full cistern in 10 hours. If all the three pipes are opened together in the
empty cistern, how much time will they take to fill the cistern completely?
S o l u t i o n :
Time taken by tap A to fill the cistern = 12 hoursTime taken by tap B to fill the cistern = 15 hoursLet C be the outlet that can empty the cistern in 10 hours. Time taken by tap C to empty the
Q u e s t i o n : 2 8
A cistern can be filled by a tap in 4 hours and emptied by an outlet pipe in 6 hours. How long will it take to fill the cistern if both the tap and the pipe are opened together?
S o l u t i o n :
Time taken by the tap to fill the cistern = 4 hours ? Tap fills 
1
4
th part of the cistern in 1 hour. Time taken by the pipe to empty the cistern = 6 hours ? Pipe empties out 
1
6
th part of the cistern