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?

On what sum will the compound interest (in ₹) for $2 \frac{1}{2}$ years at $10 \%$ per annum amount to ₹ $6352.50$?

The simple interest accrued on an amount of $Rs. 20000$ at the end of $3$ years is $Rs. 7200$. What would be the compound interest accrued on the same amount at the same rate in the same period?

The difference between compound and simple interest at a certain rate on $Rs. 2000$ at the end of two years is $Rs. 12.8$. The rate of interest (in $\%$) per annum is:

$A$ man borrows ₹ $25000$ at $20 \%$ compound interest. At the end of every year,he pays ₹ $5000$ as part repayment. How much (in ₹) does he still owe after three such instalments?

The difference between simple interest and compound interest on a certain sum for $3$ years at $5 \%$ per annum is ₹ $122$. Find the sum (in ₹).