Theory of Costs and Revenue

When a business produces goods, it faces different types of costs that affect profit. Fixed costs stay the same whether production increases or not—like rent for a factory or salaries of permanent workers. Variable costs change with output; producing more items means spending more on raw materials and electricity. Total cost is simply fixed costs plus variable costs added together.

Average cost tells you the cost per unit produced. If a Lagos clothing factory spends ₦1,000,000 monthly to make 10,000 shirts, the average cost per shirt is ₦100. Marginal cost is the extra expense of producing one additional unit. Understanding these distinctions helps businesses decide whether expanding production will increase or reduce their per-unit costs.

When you're running a business, costs matter differently depending on who's asking. An accountant looks at actual money you've spent—your explicit costs. These are real cash payments like wages, rent, and materials. An economist thinks bigger. They include both explicit costs and implicit costs, which are opportunities you've given up.

Let's say you own a small provision store in Lagos. The accountant counts your rent, staff salary, and stock purchases. But an economist also considers what you could have earned if you'd invested that same money elsewhere or worked as a manager elsewhere instead. That forgone income is your opportunity cost, and it's very real economically even though you didn't write a cheque for it.

Understanding this difference helps explain why a business looks profitable to an accountant but economically unprofitable to an economist.

When economists talk about costs, they mean something different from what you see on your receipt. There are two main types: explicit costs and implicit costs. Explicit costs are the actual money you spend—like paying N5,000 for flour to bake bread. Implicit costs are opportunities you give up. If you use your time to bake instead of working a job that pays N2,000 daily, that N2,000 is your implicit cost, even though you don't physically spend it.

Think of a Lagos tailor who owns her shop. She pays rent (explicit) but also gives up the salary she could earn working elsewhere (implicit). Smart economists count both when calculating true profit. This helps business owners make better decisions about whether their venture is truly worthwhile.

In economics, the short run is when a firm cannot change all its production factors—some costs stay fixed no matter what. Think of a bakery in Lagos that has already paid rent for its shop and bought an oven. These costs don't change quickly. The long run is different; the firm can adjust everything, including moving to a bigger shop or buying new equipment. So in the short run, a bakery pays fixed rent whether it bakes ten loaves or one hundred. In the long run, if demand increases, it can expand entirely. Understanding this matters because short-run costs include both fixed costs (rent, salaries) and variable costs (flour, electricity), but long-run costs eventually become variable as the business adjusts. This is why firms behave differently depending on their time horizon.

The relationship between marginal cost (MC) and marginal revenue (MR) is crucial for understanding business profits. Marginal cost is the extra cost of producing one additional unit, while marginal revenue is the extra money earned from selling that unit. A business maximizes profit when MC equals MR—at this point, producing more units would cost more than they'd earn.

Think of a Lagos bakery making bread. When the bakery produces the 100th loaf at ₦200 cost but sells it for ₦500, the profit is ₦300 per loaf. However, if producing the 101st loaf costs ₦600 but only sells for ₦500, the bakery loses money. Wise businesses stop producing before reaching this loss point.

Understanding this relationship helps predict business decisions. When MR exceeds MC, firms expand production. When MC exceeds MR, they reduce output.

The cost and supply curve shows the relationship between the price of goods and the quantity producers are willing to supply. As production costs increase, businesses need higher prices to make profits, so they supply less. When costs decrease, they can afford to supply more at lower prices. Think of a Nigerian tomato farmer: during dry season when water is scarce, irrigation costs rise significantly, so the farmer supplies fewer tomatoes unless prices increase. During rainy season when water is free, costs drop and the farmer supplies more tomatoes even at lower prices. The supply curve slopes upward because higher prices motivate producers to increase output and enter the market. Understanding this relationship helps explain why goods become scarcer and more expensive when production becomes difficult.

Revenue simply means the money a business receives from selling its products or services. Understanding revenue concepts is crucial for UTME success.

Total Revenue is the complete amount earned from selling all units of a product. For instance, if a Lagos trader sells 100 bags of rice at ₦5,000 each, the total revenue is ₦500,000. Average Revenue is the income per unit sold—in this example, ₦5,000 per bag. Marginal Revenue represents the extra money gained from selling one additional unit. If selling the 101st bag brings in ₦4,800, that's the marginal revenue.

These three concepts work together to show how revenue changes as production increases. In perfect competition, average and marginal revenue remain constant, but in monopoly situations, they typically decrease as more units are sold because prices must drop to attract additional buyers.