$A$ money lender lends ₹ $400$ for $3$ $years$ to a person and ₹ $500$ for $4$ $years$ to another person at the same rate of simple interest. If altogether he receives ₹ $160$ as interest,what is the rate of interest per annum (in $\%$)?

If the simple interest on a certain sum of money for $2$ $years$ is one-fifth of the sum,then the rate of interest (in $\%$) per annum is

What is the simple interest (in ₹) on ₹ $5400$ in $5$ years at the rate of $12 \%$ per annum?

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

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?

During the first year,the population of a village is increased by $5 \%$ and in the second year it is diminished by $5 \%$. At the end of the second year,its population was $47880$. What was the population at the beginning of the first year?