Find the compound interest (in ₹) on ₹ $15625$ for $9$ months at $16 \%$ per annum compounded quarterly.

Find the ratio of $S.I.$ and $C.I.$ on a certain sum of money at $5 \%$ per annum for $2$ years.

The difference between the $S.I.$ and $C.I.$ obtained on a principal amount at $5$ $p.c.p.a.$ after $2$ years is $Rs. 35$. What is the principal amount (in $Rs.$)?

$A$ man borrows $Rs. 5100$ to be paid back with compound interest at the rate of $4 \%$ p.a. by the end of $2$ years in two equal yearly instalments. How much (in $Rs.$) will be each instalment?

If a sum of money placed at compound interest,compounded annually,doubles itself in $5$ years,then the same amount of money will be $8$ times of itself in how many years?

If $64000$ is deposited at $5 \%$ compound interest for a period of $18$ months,interest being compounded half-yearly,find the amount.