permutations : how many ways can 5 people (A-E) sit in a row if A must be to the left of B not not necessarily right next to each other? how many ways if A and B CANNOT sit next to eachother?

Question

anonymous · Answer

Are there any options? 
I got the first one as 24 ways. 
And the second one as 72 ways.
I could be wrong. :-|

anonymous · Answer

no its not a multiple choice

anonymous · Answer

can u justify your answers?

anonymous · Answer

Err, the first one :
_ _ _ _ B 
because A HAS to be before B.
So, it can be done in 4 * 3 * 2 * 1 ways.
The second one, 
All the number of ways that they can be arranged so that they aren't together is 12 ways.
And the other letters in 3 * 2 ways.
Therefore, 12 * 3 * 2 = 72.
:-|
That's how I did.