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:

An amount of ₹ $8000$ was deposited at simple interest for $3$ years at $7.5$ $\%$ per annum. How much more would have been gained (in ₹) had it been deposited at the same rate per cent compound interest?

Find the difference (in $Rs.$) between $C.I.$ and $S.I.$ on $Rs. 13000$ at $4 \%$ per annum for $3$ years.

In how many years will a sum of ₹ $800$ at $10 \%$ per annum compound interest,compounded semiannually,become ₹ $926.10$?

Suneeta borrowed a certain sum from Reena for $2 \,yr$ at simple interest. Suneeta lent this sum to Venu at the same rate for $2 \,yr$ at compound interest. At the end of $2 \,yr$,she received $Rs. 110$ as compound interest but paid $Rs. 100$ as simple interest. Find the sum and the rate of interest.

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