Mattias gets dressed in the dark one morning and chooses his clothes at random. He chooses a shirt (green, red, or yellow), a pair of pants (black or blue), and a pair of shoes (checkered or red). The following shows a tree diagram that shows the sample space:
 What is the probability that no part of Mattia's outfit is red?
 1/5
 1/2
 1/4
 1/3