1. The problem statement, all variables and given/known data http://www.xtremepapers.com/Edexcel/Advanced%20Level/Mathematics/Subject%20Sorted/S2/S2%202008-06.pdf [Broken] Question 1(d) 2. Relevant equations 3. The attempt at a solution So I know this is a conditional probability question. Now I would have said P(X>8) / P(X=5) because it is probability I will NOT be served (i.e: time is greater than 8 mins) given I have already waited 5 mins this gives me infinity because x/0 = inifinty How do I approach this question?