$Rs. 600$ becomes $Rs. 720$ in $4$ $years$ at simple interest. If the rate of interest is increased by $2 \%$,what will be the total amount (in $Rs.$)?

$A$ person receives a simple interest of ₹ $1,000$ on a certain principal at the rate of $5 \%$ $p.a.$ in $4$ years. What compound interest (in ₹) will that person receive on twice the principal in $2$ years at the same rate?

Alipta received some amount of money from her father. In how many $years$ will the ratio of the money (principal) and the interest obtained from it be $10: 3$ at the rate of $6 \%$ simple interest per annum?

At what percent of simple interest will a sum of money double itself in $15$ years?

What principal will amount (in ₹) to ₹ $15000$ at $10 \%$ per annum in $5$ years?

$A$ lent ₹ $6000$ to $B$ for $2$ $years$ and ₹ $1500$ to $C$ for $4$ $years$ and received altogether from both ₹ $900$ as simple interest. The rate of interest is (in $\%$):