If a sum of money at compound interest amounts to thrice itself in $3$ years, then in how many years will it be $9$ times itself?

What will be the amount (In ₹) if a sum of ₹ $5000$ is placed at compound interest for $3$ years while rate of interest for the first, second and third years is $2,3$ and $4$ per cent, respectively?

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?

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

If the difference between the simple and the compound interest earned on a sum of money at the rate of $5$ $p.c.p.a.$ for $2$ $years$ is $Rs. 16$ find the principal (In $Rs.$) ? 

A bank offers $5 \%$ compound interest calculated on half-yearly basis. A customer deposits ₹ $1600$ each on $1^{st}$ January and $1^{st}$ July of a year. At the end of the year, the amount (In ₹) he would have gained by way of interest is