What is the $S.I.$ on $Rs. 800$ at $5 \%$ per annum for $3$ years?

The population of Mumbai increases by $5 \%$ per annum. Its population was $100000$ in $2004$. What was its population after $3$ years?

₹ $1500$ is invested at a rate of $10 \%$ simple interest,and the interest is added to the principal after every $5$ years. In how many years will it amount to ₹ $2500$?

Reena took a loan of ₹ $1,200$ with simple interest for as many years as the rate of interest. If she paid ₹ $432$ as interest at the end of the loan period,what was the rate of interest?

Mr. Mani invested an amount of ₹ $12000$ at a simple interest rate of $10 \%$ $p.a.$ and another amount at a simple interest rate of $20 \%$ $p.a.$. The total interest earned at the end of one year on the total amount invested was $14 \%$ $p.a.$. Find the total amount (in ₹) invested.

If the simple interest on ₹ $x$ at a rate of $a \%$ for $m$ years is same as that on ₹ $y$ at a rate of $a^2 \%$ for $m^2$ years,then $x: y$ is equal to