Q.The cost (in rupees) of producing x items in factory, each day is given by 𝐶(𝑥) = 0.00013𝑥3 + 0.002 𝑥2 + 5𝑥 + 2200 Find the marginal cost when 150 items are produced.

Marginal Cost: The Cost of One More

Imagine you run a small bakery. Every morning you bake 50 loaves; your total cost — rent, flour, yeast, electricity, your own time — comes to ₹2,000, an average of ₹40 per loaf.

Now a customer asks for one more loaf. What does baking that 51st loaf actually cost? Not ₹40 — the rent doesn't change and your time is already paid; the oven is already hot. You need only a little more flour, yeast, and electricity: maybe ₹15.

That ₹15 is the marginal cost.

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The Core Intuition

Marginal cost answers one question: "If I produce one more unit, how much does my total cost increase?"

It is not the average cost. It is not the total cost. It is the change in total cost when output changes by exactly one unit. …