Nikhil bought $5400$ books in a month and sold $4050$ books. What per cent of books he could not sell?

A Maruti car costing $₹ 2,50,000$ dropped $23\%$ in value of the first year. How much was it worth at the end of the year?

A $4$ metre elastic band is increased by $10\%$. Find its new length.

The length of a wire is decreased by $12\frac{1}{2}\%$. What is the new length if it was $150$ metres?

In a certain year, the population of a state is $8$ crore. If it increases by $2\%$ every year, what will be its population after one year?

The speed of a car is $80 \mathrm{km}/\mathrm{hour}$. It is (i) increased by $10\%$ (ii) decreased by $10\%$. Find the new speed of the car in the two cases.

A mixture contains $70\%$ nitre, $12\%$ sulphur and rest charcoal. What is the amount of charcoal in $15 \mathrm{kg}$ of mixture?