In a certain number of years,a sum of money doubles itself at $6 \frac{1}{4} \%$ simple interest per annum. The required time (in $years$) is:

On a sum of money,the simple interest for $2$ years is ₹ $660$,while the compound interest is ₹ $696.30$,the rate of interest being the same in both the cases. The rate of interest (in $\%$) is

Divide $Rs. 2602$ between $X$ and $Y$,so that the amount of $X$ after $7 \,yr$ is equal to the amount of $Y$ after $9 \,yr$,the interest being compounded at $4 \%$ per annum.

The value of a machine depreciates at the rate of $12\%$ per annum. It was purchased $3$ years ago. Its present value is $Rs. 29644.032$. What was the purchase price (in $Rs.$) of the machine?

At what rate per cent compound interest does a sum of money become $16$ times in $4$ years?

If $Rs. 3000$ amounts to $Rs. 4320$ at compound interest in a certain time,then what will $Rs. 3000$ amount to in half of that time (in $Rs.$)?