JAMB Economics 2015 Paper

Concept:Marginal product is the extra output gained from adding one more unit of the variable factor.Explanation:Marginal product is calculated as:$$MP = \frac{\Delta TP}{\Delta L}$$Where $\Delta TP$ is the change in total product and $\Delta L$ is the change in variable factor units.For the fifth unit, compare total product at 5 units with total product at 4 units:$$MP_5 = \frac{55 - 48}{5 - 4}$$$$MP_5 = \frac{7}{1} = 7$$Thus, the marginal product at the fifth variable factor is 7.Answer:A. 7