vector question?

[Yoda]

Let A= (5, 4, 1) and B = (3, 1, -4). M is a point on AB, such that AM=4MB. Find M 

Need help with this question thanks

[kinslayer]

OM = OA + AM = OA + 4/5 * AB (since AM = 4MB and AM + MB = AB)

Now AB = OB - OA, so OM = OA + 4/5 * (OB - OA) = 1/5 * (OA + 4 * OB)

Plug in A and B and you end up with OM = (3.4, 1.6, -3).

(pretend the vectors have pretty arrows over them. LaTeX wouldn't let me draw them for some reason).