Amit was given an increment of $20\%$ on his salary. If his new salary is $₹30600$, what was his salary before the increment?

Sonal attended her school on $204$ days in a full year. If her attendance is $85\%$, find the number of days on which the school was opened.

$A$’s income is $20\%$ less than that of $B$. By what per cent is $B$’s income more than $A$’s?

The price of petrol goes up by $10\%$. By how much percent must a motorist reduce the consumption of petrol so that the expenditure on it remains unchanged?

The population of a town increases by $8\%$ annually. If the present population is $54000$, what was it a year ago?

The value of a machine depreciates every year by $20\%$. If the present value of the machine be $₹160000$, what was its value last year?

An alloy contains $40\%$ copper, $32\%$ nickel and rest zinc. Find the mass of zinc in one kg of the alloy.

Balanced diet should contain $12\%$ of proteins, $25\%$ of fats and $63\%$ of carbohydrates. If a child needs $2600$ calories in his food daily, find in calories the amount of each of these in his daily food intake.

Gunpowder contains $75\%$ nitre and $10\%$ sulphur. Find the amount of gunpowder which carries $9 \mathrm{kg}$ nitre. What amount of gunpowder would contain $2.5 \mathrm{kg}$ sulphur?