If the annual rate of simple interest increases from $10 \%$ to $12 \frac{1}{2} \%$,a man's yearly income increases by ₹ $1250$. His principal (in ₹) is

$A$ certain sum doubles in $7$ years at simple interest. The same sum under the same interest rate will become $4$ times in how many years?

The simple interest accrued on a certain principal is ₹ $1200$ in $4$ years at the rate of $8 \%$ per annum. What would be the simple interest (in ₹) accrued on thrice of that principal at the rate of $6 \%$ per annum in $3$ years?

What is the interest (in $Rs.$) received on a principal of $Rs. 450$ for $2$ years, if the interest received on $Re. 1$ after $4$ years at the same rate of simple interest is $Rs. 0.40$?

Income of Hemant was Rs. $4000$. In the first $2$ years,his income decreased by $10\%$ and $5\%$ respectively,but in the third year,the income increased by $15\%$. What was his income (in Rs.) at the end of the third year?

What is the present worth (in ₹) of ₹ $132$ due in $2$ years at $5\%$ simple interest per annum?