What is the rate of interest (in $\%$) if simple interest earned on a certain sum for the $3^{rd}$ year is $₹ 2,000$ and compound interest earned in $2$ years is $₹ 4,160$?

$A$ sum of ₹ $1260$ is borrowed from a money lender at $10 \%$ p.a. compounded annually. If the amount is to be paid back in two equal annual instalments,find out the annual instalment (in ₹).

The production of a factory grows at a $8 \%$ $p.a.$ What will be its production (in $lakh$ tonnes) for the year $2010$,if its production in $2008$ was $70$ $lakh$ tonnes?

The compound interest on ₹ $30000$ at $7 \%$ per annum is ₹ $4347$. The period (in years) is

$A$ sum of money at compound interest doubles itself in $15$ years. It will become eight times of itself in (in $years$):

Suneeta borrowed a certain sum from Reena for $2 \,yr$ at simple interest. Suneeta lent this sum to Venu at the same rate for $2 \,yr$ at compound interest. At the end of $2 \,yr$,she received $Rs. 110$ as compound interest but paid $Rs. 100$ as simple interest. Find the sum and the rate of interest.