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

$A$ sum of ₹ $1260$ is borrowed from a money lender at $10 \%$ p.a. compounded annually. If the amount is to be paid back in two equal annual instalments,find out the annual instalment (in ₹).

What sum will give ₹ $244$ as the difference between simple interest and compound interest at $10 \%$ per annum in $1 \frac{1}{2}$ years,compounded half-yearly?

$A$ man borrows ₹ $4000$ from a bank at $7 \frac{1}{2} \%$ compound interest. At the end of every year,he pays ₹ $1500$ as part repayment of the loan and interest. How much does he still owe to the bank after three such instalments (in ₹)?

If a sum of money at compound interest amounts to thrice itself in $3$ years,then in how many years will it be $9$ times itself?

If the compound interest on a sum for $2$ years at $12 \frac{1}{2} \%$ per annum is ₹ $510$,the simple interest (in ₹) on the same sum at the same rate for the same period of time is: