The population of Mumbai increases by $5 \%$ per annum. Its population was $100000$ in $2004$. What was its population after $3$ years?

$A$ 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?

Alipta received some amount of money from her father. In how many $years$ will the ratio of the money (principal) and the interest obtained from it be $10: 3$ at the rate of $6 \%$ simple interest per annum?

The rate of interest on a sum is $4 \%$ per annum for the first $2$ years,$6 \%$ per annum for the next $4$ years,and $8 \%$ per annum for the period beyond $6$ years. If the simple interest accrued by the sum for a total period of $9$ years is ₹ $1120$,find the sum. (In ₹)

The principal (in ₹) that will yield ₹ $60$ as simple interest at $6 \%$ per annum in $5$ years is

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