There are 3 red balls and 2 blue balls. A ball is randomly selected one at a time without replacement until a red ball is selected.Find the probability that it takes 3 times to select a red ball.
Only one way to have to take 3 times to select a red ball. You have to select the two blue balls on the first two draws;
Number of all possible arrangements of draws = 5! / [2! * 3!] = 10
Probability = 1 / 10
+7 
