Mannan Miyan observed, after 6 years of taking a loan of some money, that the interest to be paid had become 3/8 th of its principal. Let us determine the rate of simple interest in per cent per annum.

Let the principal = ₹ x

Simple Interest (I) = ₹ \frac{3 x}{8} \\

Time (t) = 6 years

Rate (r) = ?

Rate = \frac{\text { Interest } \times 100}{\text { Principal } \times \text { Time }}=\frac{\frac{3}{8} \times 100}{x \times 6} \\

=\frac{3}{8} \times \frac{100}{6}=\frac{25}{4}=6 \frac{1}{4} \\

∴ Rate =6 \frac{1}{4} \\ %