The rate percent per annum at which ₹ $1200$ amounts to ₹ $1440$ in $4$ years is:

$A$ money lender claims to lend money at the rate of $10 \%$ per annum simple interest. However,he takes the interest in advance when he lends a sum for one year. At what interest rate does he lend the money actually?

An automobile financier claims to be lending money at simple interest,but he includes the interest every six months for calculating the principal. If he is charging an interest of $10 \%$ per annum,the effective rate of interest (in $\%$) becomes:

Arun invested a sum of money at a certain rate of simple interest for a period of $4$ years. Had he invested the same sum for a period of $6$ years,the total interest earned by him would have been $50\%$ more than the earlier interest amount. What was the rate of interest per cent per annum?

Prakash lends a part of ₹ $20,000$ at $8 \%$ simple interest and the remaining at $\frac{4}{3} \%$ simple interest. His total income after a year was ₹ $800$. Find the sum (in ₹) lent at $8 \%$ interest.

The simple interest accrued on an amount of $Rs. 2500$ at the end of six years is $Rs. 1875$. What would be the simple interest (in $Rs.$) accrued on an amount of $Rs. 6875$ at the same rate and same period?