JAMB 2010 · UTME · Q5

At what rate will the interest on ₦400 increase to ₦24 in 3 years reckoning in simple interest?

Worked solution (try it first)

Use $I = \dfrac{PRT}{100}$ with $I = 24$ , $P = 400$ and $T = 3$ : $24 = \dfrac{400 \times R \times 3}{100}$ .
The right side simplifies to $12R$ , so $12R = 24$ .
Divide both sides by 12: $R = 2$ .
The rate is $2\%$ , option B.