# Is it possible to have constant marginal cost and decreasing average cost simultaneously? [closed]

I thought about possibility of occurring such event in the case of presence of fixed costs, but I would like to know others opinions.

## closed as off-topic by Herr K., luchonacho, Giskard, Adam Bailey, jmbejaraOct 4 '17 at 0:23

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question does not meet the standards for homework questions as spelled out in the relevant meta posts. For more information, see our policy on homework question and the general FAQ." – Herr K., luchonacho, Giskard, Adam Bailey, jmbejara

Decreasing average cost implies that marginal cost is less than average cost ($MC<AC$, which can be proved by simply taking the first derivative of $C(q)/q$). With constant marginal cost, there exists a simple linear cost function $C(q)=F+a\times q$ that satisfies the constant $MC$ condition, where the constant $F$ is the fixed cost and $a \times q$ is the variable cost, and the constant $a$ is $MC$. Therefore $AC=F/q+a$ is greater than $MC=a$.