There are 20 balls in a jar. You take out 2 blue balls without putting them back inside, and now the probability of pulling out a blue ball is 1/5. How many blue balls were there in the beginning?
Options:
(A) 12.
(B) 9.
(C) 8.
(D) 7.
(E) 6. Think first, then make a decision. Some random thoughts:
12 = 3 blue balls + 18 / 2 So the answer is (A).