A drawer is filled with 2 black shirts, 7 white shirts, and 11 gray shirts. One shirt is chosen at random from the drawer. Find the probability that it is not a black shirt.

Answer 1

20 in drawer
2 black
probability black yes =2/20 = 0.10
so
probability black no = 1.00 - 0.10

Answer 2

The drawer is filled with 2 + 7 + 11 = 20 shirts.
There are 7 + 11 = 18 shirts that are not black.
A shirt is chosen at random. This means that each shirt is equally likely to be chosen.
You would need to divide your number of shirts that are not black by all your shirts

So, here is the probability that the chosen shirt is not black.
not black
The fraction 18/20 can be simplified to 9/10 .

9/10 would be your answer