At what rate per annum will the simple interest on Rs. $550$ be Rs. $33$ in $3$ years?

The formula for simple interest is:
$$\text{SI}=\frac{P\times R\times T}{100}$$
Given:Principal ($P$) = Rs. $550$ Simple Interest ($\text{SI}$) = Rs. $33$ Time ($T$) = $3$ yearsSubstitute the values to find the rate ($R$):
$$33=\frac{550\times R\times 3}{100}$$
$$33=\frac{1650\times R}{100}$$
$$33=16.5\times R$$
$$R=\frac{33}{16.5}=2\%$$
Thus, the rate of interest is $2\%$ per annum.