Question

In the new budget, the price of petrol rose by 10%. By how much percent must one reduce the consumption so that the expenditure does not increase?

Answer 1

We have to reduce the consumption such that the expenditure does not increase.
For this, we use the following formula:
\[\left( \frac{r}{r + 100} \right) \times 100,\text{ where r = percentage rise in the price of the commodity }\]
\[ \therefore\text{ Percentage reduction in the consumption }= \left( \frac{10}{10 + 100} \right) \times 100 = \left( \frac{10}{110} \right) \times 100 ( \because r = 10 \% )\]
\[ = 9\frac{1}{11}\]