The price (per litre) of petrol increases by 70%. By what percent should its consumption be reduced such that the expenditure on it increases by 19% only?

Correct option is B

Given:

Petrol price per litre increases by 70%

Desired increase in expenditure is only 19%

Formula Used:

Expenditure is the product of price and consumption:

Expenditure = Price × Consumption

Solution:

Let:

Original price = 100

Original consumption = 100

=>Original expenditure = 100 × 100 = 10,000

New price = 100 + 70 = 170

New expenditure = 10,000 × 1.19 = 11,900

New consumption = $$\frac{11900}{170}$$​ = 70

Reduction = 100 - 70 = 30

Required reduction % = $$\frac{100 - 70}{100} \times 100 = 30\%$$ 

Alternate Solution: ​

Required reduction% = $$\frac{170 - 119}{170}\times100 = 30\%$$​​