Question

How many percent should the use of milk be increased if the price of milk is

decreased by 20% so that the expenditure remains unchanged ?​

Answer 1

Answer:

Approach 1

Use relation :

Net change = A + B + AB/100

Here A = 20% , B is unknown and net change = 0

Net change = 20 + B + 20B/100 = 0

=> 20 + B + B/5 = 0

=> 100 = -6B

B = -50/3 = -16.67%

Approach-2

Increase in one variable by 1/x th will lead to a decrease of 1/(x + 1) th in other variable if product of the two variables is constant.

This is a universal rule.

So , 20% or 1/5th increase in price of milk will be accompanied by 1/6 th or 16.67% reduction in consumption to keep expenditure constant.

Approach-3

School Method :

Expenditure = Price x Quantity

Let original price of milk is Rs 100 per litre and original quantity of milk = 36 litres

Original Expenditure = Rs 3600

New price of milk after 20% increase is Rs 120 per litre

Since expenditure is same, new quantity is 3600/120 = 30 litres.

Decrease in consumption is 36 - 30 = 6 litres.

=> Percentage decrease = 6/36 x 100 =16.67%

Answer 2

Answer:

increase in consumption of milk is 25%