Which of the following pairs of quantities are in inverse proportion? (i) The number of taps filling a water tank and the time Class 8

Which of the following pairs of quantities are in inverse proportion? (i) The number of taps filling a water tank and the time Class 8

Question 1.

Which of the following pairs of quantities are in inverse proportion? Class 8

(i) The number of taps filling a water tank and the time taken to fill it.

(ii) The number of painters hired and the days needed to paint a wall of fixed size.

(iii) The distance a car can travel and the amount of petrol in the tank.

(iv) The speed of a cyclist and the time taken to cover a fixed route.

(v) The length of cloth bought and the price paid at a fixed rate per metre.

(vi) The number of pages in a book and the time required to read it at a fixed reading speed.

Solution:

(i) is inverse proportion.

(ii) is inverse proportion.

(iii) is not inverse proportion.

(iv) is inverse proportion.

(v) is not inverse proportion.

(vi) is not inverse proportion.

Question 2.

If 24 pencils cost ₹ 120, how much will 20 such pencils cost? Class 8

Solution:

Let cost of 20 pencils be ₹ x.

It is a direct proportion.

So, 24 : 20 : : 120 : x

or 24 × x = 20 × 120

or x = [latex]\frac{20 \times 120}{24}[/latex] = 20 × 5 = ₹ 100