Question

The price of petrol rose by $10\%$,by how much per cent must the consumption of petrol be reduced so that the expenditure on petrol remains the same.

Answer 1

Suppose we bought $100$ units of petrol for $₹100$.

Due to the $10\%$ rise in price, $100$units of petrol will be available for $₹110$

Now for$₹110$, the quantity of petrol available$=$$100$units

Now for $₹100$, the quantity of petrol available$=$$\frac{100}{110}\times 100$

$$\begin{gathered} =\frac{1000}{11} \\ =90.90 \end{gathered}$$

Difference in consumption $$\begin{gathered} =\left(100-90.90\right)\% \\ =9.09\% \end{gathered}$$

Hence, the consumption of petrol is to be reduced by $9.09\%$.