If the amount is $6 \frac{1}{4}$ times the principal after $2$ years at compound interest,the rate of interest (in $\%$) per annum is

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 $\%$)?

Find the least number of complete years in which a sum of money put out at $20 \%$ compound interest will be more than double?

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?

Find the difference between $S.I.$ and $C.I.$ (in $Rs.$) at $14 \%$ per annum for $2$ years on a principal of $Rs. 10000$.

$A$ man gave $50 \%$ of his savings of ₹ $84,100$ to his wife and divided the remaining sum among his two sons $A$ and $B$ of $15$ and $13$ years of age respectively. He divided it in such a way that each of his sons,when they attain the age of $18$ years,would receive the same amount at $5 \%$ compound interest per annum. The share of $B$ was (in ₹):