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 increases

Answer 1

Let price of petrol be $Rs.100$.

After increasing,

Price of petrol $=100+\frac{10}{100}\times 100=Rs.110$

Now, to keep same expenditure, the consumption should be reduced by $x\%\left(\text{say}\right)$.

Now,

$x=\frac{110-100}{110}\times 100$

$\Rightarrow x=\frac{10}{110}\times 100\approx 9\%$

Hence, to keep same expenditure, the consumption should be reduced by $9\%$.