Nikita invested ₹ $8000$ for $3$ years at $5 \%$ $C.I.$ in a post office. If the interest is compounded once in a year,what sum (in ₹) will she get after $3$ years?

$A$ bank offers $5 \%$ compound interest calculated on a half-yearly basis. $A$ customer deposits $Rs. 1600$ each on $1^{st}$ January and $1^{st}$ July of a year. At the end of the year,the amount (in $Rs.$) he would have gained by way of interest 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 compound interest on a sum of money for $3$ years at $5 \%$ per annum is ₹ $1324.05$. What is the simple interest (in ₹)?

$A$ certain sum will amount to ₹ $12,100$ in $2$ years at $10 \%$ per annum of compound interest,interest being compounded annually. The sum is (In ₹)

$A$ person takes a loan of ₹ $10,000$ at an interest rate of $10 \%$ compounded annually for a period of $4$ years. How much interest (in ₹) does he have to pay?