Finishing Halo 3 Campaign - Legendary?

[austen p]

Must I do it by myself or can I do it in co-op campaign. I want the achievments for finishing it on legendary.

 

[Rhys J]

It can be on either co-op or solo

But even if you done it like this

Mission 1-4 Solo, Mission 5-7 Co-op, Mission 8 Solo, Mission 9 Co-op, All on legendary, you still get the achievement