What is the probability that her first pick was a black sock but her second pick was a blue socks?

Question

A woman who goes to work long before sunrise every morning gets dressed in the dark.
In her sock drawer she has 9 black and 12 blue socks.
What is the probability that her first pick was a black sock but her second pick was a blue socks?

Answer 1

Probability of first picking black socks = 9/21
Probability of picking blue socks next = 12/20
Required Probability = (9/21)*(12/20) = (3/7)*(3/5) = 9/35 => 25.71%.