A sum of money was divided into 2 parts in the ratio 2:5. First part was invested for 2 years at the annual interest rate of 20% compounded annually. At what rate of simple interest per annum the second part must be invested for 2 years, so that the interest earned in both cases is the same?

Ratio = $2:5 \;\Rightarrow\; \tfrac{2S}{7}, \tfrac{5S}{7}$
CI on $\tfrac{2S}{7}$ for 2 yrs @ $20\% =$ $0.44 \times \tfrac{2S}{7} = \tfrac{0.88S}{7}$
SI on $\tfrac{5S}{7}$ for 2 yrs @ $R\% =$ $\dfrac{5S}{7} \times \dfrac{R \times 2}{100} = \dfrac{RS}{70}$
Equating ⇒ $\tfrac{0.88S}{7} = \dfrac{RS}{70}$
$\therefore \; R = 8.8\% \; \text{p.a.}$