THEORY OF COST AND REVENUE

Think of cost as money a business spends to produce goods. Total cost is simply all money spent—both what stays the same and what changes. Fixed costs never change, like rent for a factory or teacher salaries that a school pays monthly whether production happens or not. Variable costs change with production levels; the more you produce, the higher these costs become. For instance, a bakery in Lagos pays the same rent whether it bakes fifty or five hundred loaves daily, but flour and yeast costs rise as production increases.

Average cost tells you the cost per unit produced—divide total cost by quantity made. Marginal cost is the extra cost of producing just one more unit. These concepts help businesses decide how much to produce profitably.

The short run is a period where a business cannot change all its production factors. A bakery in Lagos, for example, cannot quickly build a new factory or buy additional ovens, so it works with fixed costs like rent and existing equipment. Variable costs like flour and yeast change with output. The long run, however, is a period long enough for the business to adjust everything—it can build that new factory or buy more ovens. This means all costs become variable in the long run. Understanding this matters because in the short run, firms face limitations, but in the long run, they have flexibility to expand or contract operations. Short run costs include both fixed and variable costs, while long run costs give businesses the freedom to optimize their entire production setup. This distinction helps explain why firms behave differently depending on time horizons.

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The accountant and economist look at costs differently, and understanding this difference is crucial for your WAEC exam. An accountant focuses only on actual money paid out—explicit costs. For example, if a business pays ₦500,000 for rent, that's what gets recorded. However, an economist considers both explicit costs AND implicit costs, which are opportunity costs. These are earnings you give up by choosing one option over another.

Consider a Nigerian trader who leaves a ₦200,000 monthly job to run a shop. The accountant counts only the shop's actual expenses. But the economist adds that ₦200,000 as an implicit cost because it's the income sacrificed. This makes the economist's total cost higher than the accountant's. The economist's profit will therefore be lower because it accounts for what you've given up.

Every choice you make has a cost beyond what you pay in naira. Opportunity cost is the value of the next best alternative you give up when making a decision. Money cost, on the other hand, is the actual cash you spend on something.

Think about it this way: if you use ₦5,000 to buy textbooks instead of attending a wedding ceremony, your money cost is ₦5,000. But your opportunity cost includes missing the social gathering and the gift-giving experience. Both costs matter in economics.

Consider a farmer with one hectare of land. Planting cassava costs him ₦50,000 in seeds and labour. But if he chooses cassava over yams, which would earn ₦80,000, his opportunity cost is ₦80,000—the profit he lost. Money cost alone doesn't tell the complete story.

Understanding this difference helps you make better economic decisions and analyse business choices critically.

Marginal revenue is the additional income a business gets from selling one extra unit of output. Think of it as the money gained from that next sale. When a trader in Lekos market sells more tomatoes, the revenue from that final basket is the marginal revenue.

As production increases, marginal revenue typically falls because businesses must reduce prices to sell more units. A phone seller in Lagos might earn ₦50,000 from their 10th phone sold, but only ₦45,000 from the 20th phone because they've had to lower prices to attract more buyers.

The relationship between marginal revenue and marginal cost determines profit-maximizing output. When marginal revenue equals marginal cost, that's the sweet spot for maximum profit—not before, not after.