WAEC - Economics (2015 - No. 17)

Marginal utility is the additional satisfaction a consumer gains from consuming one more unit of a good or service.  As a consumer consumes more units of a product, the marginal utility derived eventually drops. This relates with the law of diminishing marginal returns which states that, there will be a decrease in the marginal output of a production process as the amount of a single factor of production is incrementally increased, while the amounts of all other factors of production stay constant.