$A$ 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 $Rs. 3840$ 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?

Sita deposited ₹ $5,000$ at $10\%$ simple interest for $2$ years. How much more money (in ₹) will Sita have in her account at the end of two years,if it is compounded semi-annually?

Which information given below is sufficient to know the principal amount if the difference between the $C.I.$ and $S.I.$ for $2$ years is $18$?
$(I)$ The rate is same at which an amount of $Rs. 1000$ becomes $1120$ in $2$ years under $S.I.$
$(II)$ The principal is $Rs. 2000$.

Find the least number of complete years in which a sum of $Rs. 1500$ at $25 \%$ compound interest will be more than double.