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Chapter 9

Unitary Method — Mental Maths

Class - 6 RS Aggarwal Mathematics Solutions



Exercise 9(B) - Mental Maths

Question 1

Fill in the blanks:

(i) Less is the number of articles, the ___________ will be their value.

(ii) The total cost vary ___________ as the number of articles bought.

(iii) A man saves ₹6000 in a year. His savings in 3 months is ₹ ___________

(iv) If the cost of 6 pens is ₹102, then the cost of 8 pens is ₹ ___________

(v) If a car consumes 6 litres of petrol in covering 111 km, then in 1 litre it covers ___________ km.

Answer

(i) Less is the number of articles, the less will be their value.

(ii) The total cost vary directly as the number of articles bought.

(iii) Savings in 12 months = ₹ 6000

Savings in 1 month = ₹ (600012)\Big(\dfrac{6000}{12}\Big) = ₹ 500

Savings in 3 months = ₹ (500 x 3) = ₹ 1500

(iv) Cost of 6 pens = ₹ 102

Cost of 1 pen = ₹ (1026)\Big(\dfrac{102}{6}\Big) = ₹ 17

Cost of 8 pens = ₹ (17 x 8) = ₹ 136

(v) In 6 litres, the car covers = 111 km

In 1 litre, the car covers = (1116)\Big(\dfrac{111}{6}\Big) km = 18.5 km

Question 2

Write (T) for true and (F) for false for each of the following statements:

(i) More is the number of articles, more will be their value. ___________

(ii) More men at work, more is the work done. ___________

(iii) More men at work, less will be the time taken to finish a piece of work. ___________

(iv) If 5 men can finish a work in 15 days, then 1 man can finish it in 3 days. ___________

(v) More is the speed of a car, more will be the time taken to cover a fixed distance. ___________

Answer

(i) T

Cost of articles is directly proportional to the number of articles.

(ii) T

Work done is directly proportional to the number of men at work.

(iii) T

More men at work will finish the work in less time.

(iv) F

Fewer men at work will take more time. So, 1 man can finish the work in (15 x 5) = 75 days, not 3 days.

(v) F

More is the speed of a car, less will be the time taken to cover a fixed distance.

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