$A$ sum of money lent out at simple interest amounts to $Rs. 720$ after $2$ years and $Rs. 1020$ after a further period of $5$ years. Find the principal (in $Rs.$).

Peter invested an amount of ₹ $12,000$ at the rate of $10 \%$ $p.a.$ simple interest and another amount at the rate of $20 \%$ $p.a.$ simple interest. The total interest earned at the end of one year on the total amount invested became $14 \%$ $p.a.$ Find the total amount (in ₹) invested.

Simple interest on a certain sum is $\frac{16}{25}$ of the sum. If the rate per cent and time (in years) are equal,then the rate per cent is:

$A$ 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?

$A$ man invests ₹ $3965$ in the names of his three daughters,Neeta,Sita,and Gita,in such a way that they would receive the same amount after $2, 3,$ and $4$ years. If the rate of interest is $5 \%$ p.a.,then the amount (in ₹) invested for Neeta,Sita,and Gita is:

If the difference between the simple interest on a certain sum for $4$ $years$ at $2 \frac{1}{2} \%$ per annum and the simple interest on the same sum for the same period at $3 \%$ per annum is ₹ $60$,then the sum (in ₹) is: