# market equilibrium quantity $\ne$ firm profit maximising quantity?

Consider a perfectly competitive market with equilibrium price $P_{eq}$ and quantity $Q_{eq}$ and firm with profit maximising quantity $Q_f$ as illustrated below:

I guess any firm in the market would have the same demand, marginal revenue and average revenue (or am I wrong?), but what about profit maximising quantity $Q_f$? It seems to depend on $MC$. Is $MC$ different for each firm?

1. If so, then $Q_f$ is not necessarily the same for each firm?

2. If not, why?

• This part: "any firm in the market would have the same demand" is not clear to me. The industry faces demand, not individual firms. Aug 11 '16 at 14:46
• @denesp The MR for each firm is equal to the equilibrium price determined by the market right?
– BCLC
Aug 12 '16 at 3:29
• In a competitive market? Yes. I don't see what this has to do with demand though. Aug 12 '16 at 7:59