Jar contains 10 red marbles and 30 blue marbles. A random sample of n = 3 marbles is selected from the jar. If

A jar contains 10 red marbles and 30 blue marbles. A random sample of n = 3 marbles is selected from the jar. If the first two marbles are both blue, what is the probability that the third marble will be red?
a. 10/37
b. 10/38
c. 10/40
d. 8/38

After the first two balls are drawn there are 38 balls left of which 10 are red and 28 are blue.
Thus probability third ball is red is 10/38
ie. answer b

10/38