$A$ sum of money doubles itself in $8$ years. In how many years will it treble?

$A$ lends ₹ $2500$ to $B$ and a certain sum to $C$ at the same time at $7 \%$ $p.a.$ simple interest. If after $4$ $years,$ $A$ altogether receives ₹ $1120$ as interest from $B$ and $C,$ then the sum lent (in ₹) to $C$ is

$A$ 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) $(T)$.

$A$ man invested $\frac{1}{3}$ of his capital at $7 \%$,$\frac{1}{4}$ at $8 \%$,and the remainder at $10 \%$. If the annual income is ₹ $561$,the capital (in ₹) is:

Ram deposited a certain sum of money in a company at $12 \%$ per annum simple interest for $4$ years and deposited an equal amount in a fixed deposit in a bank for $5$ years at $15 \%$ per annum simple interest. If the difference in the interest from the two sources is $Rs. 1350$,then the sum (in $Rs.$) deposited in each case is:

According to a census report,the population growth rate of Faridabad is going to be an increasing $A.P.$ with the first year's rate as $5 \%$ and common difference as $5 \%$,but simultaneously the migration rate is an increasing $G.P.$ with the first term as $1 \%$ and common ratio of $2$. If the population on $31 \, \text{December}, 2010$ is $1 \, \text{million}$,then find in which year will Faridabad witness its first fall in population?