If the price of oil is increased by 45%, then by what percentage should a family reduce its consumption so that the expenditure remains the same?

Correct option is C

Given:

Price increases by 45%

Expenditure must remain constant​​

Solution:

​$$\text{Reduction} = \frac{45}{100 + 45} \times 100 = \frac{45}{145} \times 100 = 31\frac1{29}\%$$

Alternate Method:

​Price increases by 45% = $$\frac{45}{100}=\frac{9}{20}$$

Price $$\times$$ Consumption = Expenditure

If Expenditure is constant 

Then,

Price $$\propto \frac 1{\text{Consumption}}$$

Price                     20       29

Consumption        29       20

Reduction = $$\frac {9}{29}\times100 =31\frac 1{29}$$ %​