$A$ sum was doubled with $12 \frac{1}{2} \%$ rate of simple interest per annum. The time taken (in years) for that sum is:

The difference between the interest received from two different banks on $₹ 5,000$ for $2$ $years$ is $₹ 25$. The difference between their rates is (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.

Arun invested a sum of money at a certain rate of simple interest for a period of $4$ years. Had he invested the same sum for a period of $6$ years,the total interest earned by him would have been $50\%$ more than the earlier interest amount. What was the rate of interest per cent per annum?

An automobile financier claims to be lending money at simple interest,but he includes the interest every six months for calculating the principal. If he is charging an interest of $10 \%$ per annum,the effective rate of interest (in $\%$) becomes:

If the interest on ₹ $800$ is more than the interest on ₹ $400$ by ₹ $40$ in $2$ years,then the rate of interest (in $\%$) per annum is: