JAMB Mathematics 2010 Paper

Concept:Direct proportion means $W = kU$, where $k$ is the constant of proportionality.To find the unknown value of $U$, first determine $k$ using the given pair of values.Explanation:Since $W$ is directly proportional to $U$, we can write:$$W = kU$$When $W = 5$ and $U = 3$, substitute into the equation:$$5 = k \times 3$$Solve for $k$:$$k = \frac{5}{3}$$Now substitute $W = \frac{2}{7}$ into $W = kU$:$$\frac{2}{7} = \frac{5}{3} \times U$$Make $U$ the subject:$$U = \frac{\frac{2}{7}}{\frac{5}{3}}$$Simplify by multiplying by the reciprocal:$$U = \frac{2}{7} \times \frac{3}{5}$$$$U = \frac{6}{35}$$Answer:$$U = \frac{6}{35}$$The correct option is A.