Vexing Velites

Hm.

I've conflicting info here.

Some sources give me a figure of 1200 Velites per legion.

Another tells me that every century of Hastati had 60 men plus an additional 20 Velites. Two centuries per maniple gives me 40 Velites for every 120 Hastati and thus in a legion with ten Maniples of Hastati, there ought to be 400 Velites rather than 1200.

I think I'm missing something really obvious.

Can anyone tell me what?