What time (in years) is taken by a sum of $Rs. 7000$ to become $Rs. 10500$ at the rate of $5 \%$ per annum simple interest?

Mr. Mani invested an amount of ₹ $12000$ at a simple interest rate of $10 \%$ $p.a.$ and another amount at a simple interest rate of $20 \%$ $p.a.$. The total interest earned at the end of one year on the total amount invested was $14 \%$ $p.a.$. Find the total amount (in ₹) invested.

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:

David invested a certain amount in three different schemes $A, B$ and $C$ with the rate of interest $10 \% \text{ p.a.}, 12 \% \text{ p.a.}$ and $15 \% \text{ p.a.}$ respectively. If the total interest accrued in one year was ₹ $3200$ and the amount invested in scheme $C$ was $150 \%$ of the amount invested in scheme $A$ and $240 \%$ of the amount invested in scheme $B$, what was the amount (in ₹) invested in scheme $B$?

$A$ man invested $\frac{1}{3}$ of his capital at $7 \%$,$\frac{1}{4}$ at $8 \%$,and the remaining at $10 \%$ rate of simple interest. If his annual income from interests is ₹ $561$,then the total capital invested (in ₹) was:

In what time will ₹ $8100$ produce the same income at $3 \%$ as ₹ $225$ in $4$ years at $3 \%$?