The least number of complete years in which a sum of money put out at $20 \%$ compound interest will be more than doubled is

$A$ certain sum of money at compound interest grows up to ₹ $12960$ in $2$ years and up to ₹ $13176$ in $3$ years. Find the rate per cent per annum.

The compound interest (in ₹) on ₹ $6250$ at $12 \%$ per annum for $1$ year,compounded half-yearly is

Which of the statements given below are sufficient to answer the following question?
What is the rate of interest per annum on an investment of $Rs. 800$?
$(I)$ The income from $S.I.$ at the end of $3$ years at the same rate of interest is $19$.
$(II)$ $C.I.$ is $15.76$ more than $S.I.$ on the same sum and same rate in $2$ years.

An amount of money at compound interest grows up to $Rs. 3840$ in $4$ $years$ and up to $Rs. 3936$ in $5$ $years$. Find the rate of interest (in $\%$)?

The compound interest accrued on an amount at the end of $3$ $years$ at $15$ $p.c.p.a.$ is $Rs. 6500.52$. What is the principal amount (in $Rs.$)?