$A$ sum of money placed at compound interest doubles itself in $4$ $years$. In how many $years$ will it amount to four times itself?

$A$ 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 ₹):

If the compound interest on a certain sum for $2$ years is ₹ $105$ and simple interest is ₹ $100$,then the sum (in ₹) is:

$A$ sum of ₹ $15000$ deposited at compound interest becomes double after $5$ $years$. After $20$ $years$,it will become (in ₹):

The difference between the compound interest and the simple interest on ₹ $8000$ for $3$ years at $5 \%$ per annum is (in ₹):

The sum for $2$ years gives a compound interest of ₹ $3225$ at the rate of $15 \%$ per annum. The principal amount is (in ₹):