JAMB 1997 · UME · Q8

Find the simple interest rate per cent per annum at which ₦1000 accumulates to ₦1240 in 3 years.

Worked solution (try it first)

The interest is the amount minus the principal: $1240 - 1000 =$ ₦240.
Use $R = \dfrac{100I}{PT}$ with $I = 240$ , $P = 1000$ and $T = 3$ : $R = \dfrac{24\,000}{3000} = 8$ .
So the rate is $8\%$ per annum, option B.