Question

A bag has five red marbles, six blue marbles, and four black marbles. What is the probability of picking a blue marble, replacing it, and then picking a black marble?

Answer 1

5+6+4=15
blue marble = 6 out of 15
replacing blue marble for black = 4 out of 14

Answer 2

P(blue) = 6/15
P(black) = 4/15
$P(blue\ then\ black)=\frac{6}{15}\times\frac{4}{15}=\frac{8}{75}$
The required value of probability is 8/75.