In what time (in $years$) will a sum of money double itself at the rate of $20 \%$ per annum simple interest?

If the simple interest on a certain sum of money after $6 \frac{1}{4}$ years is $\frac{3}{8}$ of the principal,then the rate of interest (in $\%$) per annum is

The annual payment of $Rs. 160$ in $5 \, \text{years}$ at $5 \%$ per annum simple interest will discharge a debt of (in $Rs.$):

$A$ man buys a watch for ₹ $1950$ in cash and sells it for ₹ $2200$ at a credit of $1$ $year$. If the rate of interest is $10 \%$ $p.a.$,what is his profit or loss?

Mayuri took a loan at a simple interest rate of $6 \, p.c.p.a.$ in the first year,and the rate increased by $1.5 \, p.c.p.a.$ every year. If she paid $Rs. 8190$ as interest at the end of $3 \, years$,what was her loan amount (in $Rs.$)?

What amount (in $Rs.$) would a man have received on a principal of $Rs. 4000$ after $2$ years at a simple interest rate of $5$ $p.c.p.a.$?