$A$ certain sum is invested for $T$ years. It amounts to ₹ $400$ at $10 \%$ $p.a.$. But,when invested at $4 \%$ $p.a.$,it amounts to ₹ $200$. Find the time (in years) $(T)$.

$A$ sum of money becomes $Rs. 1100$ in $2$ years and $Rs. 1400$ in $6$ years at $S.I.$ Find the rate percent.

The population of a town is $11200$. It increases by $25\%$ in the first year and decreases by $15\%$ in the second year. What is the population of the town at the end of $2$ years?

An amount fetched a total simple interest of ₹ $3200$ at the rate of $6.25 \%$ per year in $4$ years. What is the amount (principal) in ₹?

$A$ sum of $Rs. 2540$ is lent out in two parts,one at $12 \%$ and the other at $12.5 \%$. If the total annual return on the total money invested is $Rs. 312.42$,find the money (in $Rs.$) lent at $12 \% \text{ p.a.}$

In what time (in $years$) will a sum of money double itself at the rate of $20 \%$ per annum simple interest?