When $x$ units are being made, the marginal cost $C'(x)$ is approximately the cost of what?

Explanation

1. 01

   $C'(x) \approx \frac{C(x + 1) - C(x)}{1}$, the extra cost when output rises by one unit.

2. 02

   So it is roughly the cost of the $(x + 1)$th unit.