$A$ 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) $(T)$.

At what rate per cent of simple interest will a sum of money double itself in $12$ years?

If ₹ $500$ amounts to ₹ $725$ at $9 \%$ simple interest in some time,what will ₹ $600$ amount (in ₹) to at $11 \%$ in the same time?

If the difference between the simple interest on a certain sum for $4$ $years$ at $2 \frac{1}{2} \%$ per annum and the simple interest on the same sum for the same period at $3 \%$ per annum is ₹ $60$,then the sum (in ₹) is:

$A$ sum invested at $5 \%$ simple interest per annum grows to ₹ $504$ in $4$ years. The same amount at $10 \%$ simple interest per annum in $2 \frac{1}{2}$ years will grow to (in ₹):

Heena invests an amount of $10250$ at $4$ $p.c.p.a.$ to obtain a total amount of $Rs. 12710$ on simple interest after a certain period. For how many years did she invest the amount to obtain the total sum?