$A$ sum of money placed at compound interest doubles itself in $5$ years. It will amount to eight times itself at the same rate of interest in (in $years$):

An amount of money at compound interest grows up to ₹ $3,840$ in $4$ years and up to ₹ $3,936$ in $5$ years. Find the rate of interest (in $\%$).

$A$ sum of money lent at compound interest for $2 \, yr$ at $20 \% \, p.a.$ would fetch $Rs. 964$ more,if the interest was payable half-yearly than if it was payable annually. What is the sum (in $Rs.$)?

Sita deposited $Rs. 5000$ at $10\%$ simple interest for $2$ years. How much more money (in $Rs.$) will Sita have in her account at the end of $2$ years,if it is compounded semi-annually?

Rohit invested some amount at the rate of $6\%$ per annum and at the end of $3$ years he received ₹ $8730$ as simple interest. How much compound interest (in ₹) will he receive on the same amount and same rate of interest after $2$ years?

The compound interest on ₹ $30000$ at $7 \%$ per annum is ₹ $4347$. The period (in years) is