Question

A bag contains 8 yellow cubes,7 blue cubes,and 5 red cubes.If you select a cube at random,what is the probability the cube will not be blue or red

Answer 1

There are 20 total cubes. 

7/20 + 5/20 = 12/20 = probability that the cube WILL be blue or red. Can be reduced to 3/5

Therefore, the probability that the cube will NOT be blue or red is 8/20 or 2/5.

Answer 2

$|\Omega|=20\\ |A|=8\\\\ P(A)=\dfrac{8}{20}=\dfrac{2}{5}=40\%$