Question

A bag contains 4 green marbles, 3 red marbles, and 7
blue marbles. One marble is taken from the bag and put
back after checking its color. A second marble is then
taken out. What is the probability that the first is blue
and the second red?

A

B

C

D

1
13

3
26

5
7

3
28

Answer 1

Total marbles = 4 + 3 + 7 = 14.
P(first blue) = 7/14 = 1/2. P(second red) = 3/14. With replacement they’re independent, so

P(blue then red) = (7/14)·(3/14) = 21/196 = 3/28.

Answer: 3/28 (D).