A wallet contains five $10 bills, four $5 bills, and six $1 bills (nothing larger). If the bills are selected one by one in random order, what is the probability that at least two bills must be selected to obtain a first $10 bill?

Answer : Step 1 : A wallet contains five $10 bills, four $5 bills, and six $1 bills (nothing larger). $10 on the first choice is a total of 5+6=11 chances out of 4 + 5 + 6 = 15. So $10 on the first choice is a total of 11 and chances out of 15. Let the probability that at least two bills must be selected to obtain a first $10 bill. Geometric...