At what rate per cent compound interest does a sum of money become $16$ times in $4$ years?

$A$ sum of money is paid back in two annual instalments of ₹ $17,640$ each,allowing $5 \%$ compound interest compounded annually. The sum borrowed was (in ₹):

The population of a state increases by $10 \%$ every year. If its population in the year $2003$ was $15$ lakhs,what was its population in the year $2005$ (in lakhs)?

The compound interest accrued on an amount at the end of $3$ $years$ at $15$ $p.c.p.a.$ is $Rs. 6500.52$. What is the principal amount (in $Rs.$)?

The difference between the compound interest and the simple interest accrued on an amount of ₹ $18000$ in $2$ years was ₹ $405$. What was the rate of interest per cent per annum?

$A$ sum of $Rs. 1000$ after $3 \, \text{years}$ at compound interest becomes a certain amount that is equal to the amount that is the result of a $3 \, \text{year}$ depreciation from $Rs. 1728$. Find the difference between the rates (in $\%$) of $C.I.$ and depreciation? (Given $C.I.$ is $10 \% \, p.a.$)