Surely you have not given us the original question in the exact wording as it was presented to you.
If you have not then please do so at once.
If you have posted the exact question, then it is the strangest conditional probability question that I have ever seen.
Therefore, I await your reply.
Ah, I'm sorry as I was just stuck on that small part of the problem.
I have a hard time understanding why
the step from P[A∩B∩C l A∩B] to P[A∩B∩C]/P[A∩B] confuses me.
this is the full solution of the book. I can actually solve this problem and get the right answer. It's just this little transition that really confuses me