The price of a machine depreciates at the rate of r% per annum, let us find the price of the machine that was n years before.

Let us write the rate of compound interest per annum, so that the amount on ₹400 for 2 years becomes ₹441.

If a sum of money doubles itself at compound interest in n years, let us write in how many years will it become four times.

Let us calculate the principal that at the rate of 5% compound interest per annum becomes ₹615 after two years.

If the rate of increase in population is r% per year, the population after n year is p; let us find the population that was n years before.