by RonPurewal Thu Aug 01, 2013 2:00 am
hi,
this is the wrong folder for this question; you should be posting these things in the MGMAT Non-CAT folder. please do so in the future. (this thread is now locked; if you have any further questions about this problem, please post a thread in the correct folder.)
you don't have to use a probability tree diagram per se, but, whatever organizational device / thought process you decide to use is basically going to have to be equivalent to the tree.
the bare bones of the process, basically: you have to multiply the consecutive probabilities.
the probability tree is a convenient way of reminding you that you have to do this multiplication -- but, if you don't like it, you can always come up with alternative devices/frameworks.
finally, there's one totally different way to do the problem, which is to simply make a list of all the possibilities and then circle the ones that satisfy the requirement.