What is the difference between $C.I.$ and $S.I.$ on $Rs. 12000$ at $5 \%$ per annum for $2$ years?

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

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

What is the difference between the compound interests (in ₹) on ₹ $5000$ for $1 \frac{1}{2}$ years at $4 \%$ per annum compounded yearly and half-yearly?

What will be $C.I.$ (in $Rs.$) on an amount of $Rs. 10000$ at the rate of $20$ $p.c.p.a.$ in two years if the interest rate is compounded half-yearly?

What is $C.I.$ (in $Rs.$) on $Rs. 7500$ for $4$ years if the rate of interest is $10 \%$ p.a. for the first $2$ years and $20 \%$ p.a. for the next $2$ years?