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A group of workers can complete a certain job in 9 days. But it so happens that every alternate day starting form the second day, two workers are withdrawn from the job and every alternate day starting from the third day, one worker is added to the group. In such a way, the job is finished by the time, there is no worker left. If it takes the double time to finish the job now, find the number of workers who started the job?
  • a)
    5
  • b)
    10
  • c)
    15
  • d)
    20
Correct answer is option 'B'. Can you explain this answer?
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Problem Analysis:
We need to find the number of workers who started the job. We are given that a certain job can be completed by a group of workers in 9 days. But every alternate day, starting from the second day, two workers are withdrawn from the job and every alternate day, starting from the third day, one worker is added to the group. We need to determine the number of workers who started the job if it takes double the time to complete the job now.

Solution:
Let us assume that there are ‘x’ workers initially.
On the first day, all ‘x’ workers work on the job.
On the second day, ‘x-2’ workers work on the job.
On the third day, ‘x-1’ workers work on the job.
On the fourth day, ‘x-3’ workers work on the job.
On the fifth day, ‘x-2’ workers work on the job.
On the sixth day, ‘x-4’ workers work on the job.
On the seventh day, ‘x-3’ workers work on the job.
On the eighth day, ‘x-5’ workers work on the job.
On the ninth day, ‘x-4’ workers work on the job.

Total work done by ‘x’ workers in 9 days = Work done by (x-2-3+1-4+2-3+1-5+4) workers in 9 days.
= Work done by (x-9) workers in 9 days.

Let us assume that the total work to be done is ‘W’.
Then the work done in 1 day by ‘x’ workers = W/9x.
The work done in 1 day by ‘x-9’ workers = W/18(x-9).

We know that (W/9x) + (W/18(x-9)) = W.
Solving this equation, we get x = 10.

Therefore, the number of workers who started the job is 10.

Answer:
Option B - 10.
Free Test
Community Answer
A group of workers can complete a certain job in 9 days. But it so hap...
Let number of men=x then total work=9x..... (1)

as per que

let x in men starts the job

every second day -2

every third day +1

day men.

1 .x.

2. X-2

3. X-1

4. . X-3

5. X-2

6 .X-4

7. x-3

8. x-5

9. x-4

1o x-6

11. X-5

12 X-7

13. . X-6

14 X-8

15 .X-7

16 x-9

17 x-8

18 x-10

total work. 18x-90

so from 1 n 2

18x-90=9x

x=10


10 men had started the job
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A group of workers can complete a certain job in 9 days. But it so happens that every alternate day starting form the second day, two workers are withdrawn from the job and every alternate day starting from the third day, one worker is added to the group. In such a way, the job is finished by the time, there is no worker left. If it takes the double time to finish the job now, find the number of workers who started the job?a)5b)10c)15d)20Correct answer is option 'B'. Can you explain this answer?
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