Page No.9.21, Ratio Proportion And Unitary Method, Class 6, Maths RD Sharma Solutions | RD Sharma Solutions for Class 6 Mathematics PDF Download

PAGE NO 9.21:

Question 11: If a : b = 2 : 5, find the value of

ANSWER: It is given that,

a/b =  2/5  ...(1)

Now,

Question 12: The mean proportional of a and b is 10 and the value of a is four times the value of b. If a > 0, b > 0, find the value of a + b?
ANSWER: It is given that, 

From (1) and (2), 

∴ a+b=20+5 =25
Hence, a + b = 25. 

Question 13: A given quantity of rice is sufficient for 60 persons for 3 days. How many days would the rice last for 18 persons?

ANSWER: A given quantity of rice is sufficient for 60 persons for 3 days.

A given quantity of rice is sufficient for 1 person for 3 × 60 days.

A given quantity of rice is sufficient for 18 persons for  3×60/18 = 10 days. 

Hence, the rice last for 10 days for 18 persons. 

ANSWER: 12 men can reap a field in 25 days.
1 man can reap a field in 25 × 12 days.
20 men can reap a field in 25×12/20=15 days.

Hence, 20 men can reap the same field in 15 days. 

ANSWER: Let the age of Shikha be 3x and the age of Aarushi be 4x.

According to the question,

3x + 4x = 1400

⇒ 7x = 1400

⇒ x=1400/7 = 200

Hence, Shikha recieves 3 × 200 = 600 rupees
and Aarushi recieves 4 × 200 = 800 rupees. 

ANSWER: Let the weight of copper be 5x and the weight of zinc be 3x.
According to the question,
5x = 30.5 g

Hence, the weight of zinc in the alloy is 3×6.1=18.3 g

ANSWER: Let the value of A be 3x, the value of B be 5x and the value of C be 7x.

According to the question,

Hence, the value of A is 3 × 230 = Rs.690,
the value of B is 5 × 230 = Rs.1150,
and the value of C is 7 × 230 = Rs.1610.

ANSWER: 26 days are required to finish a piece of work by 40 men.
1 day is required to finish a piece of work by 40 × 26 men.
16 days are required to finish a piece of work by 40×26/16 = 65 men. 

Hence, 65 men will be needed to finish a piece of work in 16 days. 

ANSWER: Let the quantity of mango juice be 3x, the quantity of papaya juice be x and the quantity of orange juice be 4x.
According to the question,

4x=400 ml
⇒x=400/4 ml
⇒x=100 ml

(i) Quantity of mango juice = 3×100=300 ml
and Quantity of papaya juice = 100 ml
(ii) Total quantity of tropical juice = 400 + 300 + 100 = 800 ml. 

Question 20: If 48 boxes contain 6000 pens, how many such boxes will be needed for 1875 pens?

ANSWER: 48 boxes contain 6000 pens.

Number of pens contained in 1 box = 6000/48 = 125 pens.

Therefore, number of boxes needed to contain 1875 pens = 1875/125 = 15 boxes. 

Hence, 15 boxes will be needed for 1875 pens. 

Question 21: Fill in the blanks:
If 1, 2, 3 and x are in proportion, then x = .............

ANSWER:

ANSWER: Rs.2 and 50 paise = (2 × 100 + 50) paise

= 250 paise

Rs.3 and 75 paise = (3 × 100 + 75) paise

= 375 paise

Hence. Ratio of Rs.2 and 50 paise and Rs.3 and 75 paise is 2 : 3. 

Question 23: Fill in the blanks:
Mean proportion of 2 and 8 is ..........

ANSWER: Let the mean proportion of 2 and 8 be x.
Then,

Hence, mean proportion of 2 and 8 is 4. 

ANSWER: It is given that,

Hence, a : c = 8 : 15. 

ANSWER: It is given that,
2x = 5y         ......(1)
Now,