$A$ 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 $Rs.$).

$A$ certain sum of money amounts to ₹ $918$ in $2$ $years$ and ₹ $969$ in $3.5$ $years$ at simple interest. What is the rate of interest (in $\%$ $p.a.$)?

₹ $8000$ amounts to ₹ $9200$ in $3$ years at simple interest. If the interest rate is increased by $3 \%$,to how much would it amount (in ₹)?

At what rate per cent per annum will a sum of money double in $16$ years (in $.25$)?

$A$ sum of money will double itself in $16$ years at simple interest at an yearly rate of (in $\%$):

$A$ sum of ₹ $2800$ is divided into two parts in such a way that the interest on both the parts is equal. If the first part is lent at $9 \% \text{ p.a.}$ for $5 \text{ years}$ and the second part is for $6 \text{ years}$ at $10 \% \text{ p.a.}$,find the two sums.