WAEC Mathematics 2017 Paper

Concept:To combine two ratios that share a common quantity, make the common quantity equal in both ratios.Explanation:Tunde's age to Ola's age is $1:2$.Multiply both sides by $2$ to rewrite it as $2:4$.This keeps the ratio unchanged, and Ola’s share becomes $4$.Ola’s age to Musa’s age is already $4:5$.Now Ola is represented by $4$ in both ratios.So the combined ratio is $\text{Tunde}:\text{Ola}:\text{Musa} = 2:4:5$.Therefore, the ratio of Tunde’s age to Musa’s age is $2:5$.In fraction form, $\frac{\text{Tunde}}{\text{Musa}} = \frac{2}{5}$.Answer:The ratio of Tunde’s age to Musa’s age is $2:5$, which is option C.