Reena took a loan of ₹ $1,200$ with simple interest for as many years as the rate of interest. If she paid ₹ $432$ as interest at the end of the loan period,what was the rate of interest?

₹ $8000$ amounts to ₹ $9200$ in $3$ years at simple interest. If the interest rate is increased by $3 \%$,to how much would it amount (in ₹)?

$A$ 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?

The rate of simple interest (in $\%$) for which a sum of money becomes $5$ times of itself in $8$ years is:

Gaurav borrowed $Rs. 800$ at $6 \%$ and Naresh borrowed $Rs. 600$ at $10 \%$. After how much time will they both have equal debts?

$A$ sum of ₹ $8000$ is divided into two parts. The simple interest on the first part at the rate of $21 \%$ per annum is equal to the simple interest on the second part at the rate of $35 \%$ per annum. What is the interest (in ₹) of each part?