1. The problem statement, all variables and given/known data The probability of a student losing his library card is X each time he goes to the library. He goes to a different library 5 times a week, starting from Monday and ending on Friday. 1)At the end of the day on Thursday, he finally checks his wallet and realizes his library card is gone! What is the probability that the student lost his library card on Thursday and not any other day? 2)Which Library should he go to to search for his library card? 3. The attempt at a solution Is this the correct process? First see each day is mutually exclusive since once you lose the card that's it. You can't lose it on another day. 1) P(T)=Probability of losing card on Thursday = (1-X)(1-X)(1-X)(X) P(L)=Probability of him losing the card in those 4 days= 1-[(1-X)(1-X)(1-X)(1-X)] P(T|L)=Probability of him losing the card on Thursday, given that he lost the card = [(P(T)]/P[L) the answer were looking for 2) Doesn't matter which one he goes to, since the probability for each day is always X. Any help is appreciated. It concerns me a bit I find introductory probability harder than Calc III.