Answer:
Probability of the chosen T-shirt not being black will be equal to 9/10
Explanation:
In order to solve this we need to understand that probaility is equal to the number of those outcomes that we want divided by the total number of outcomes. In our case the total number of outcomes is 20 (2 + 7 + 11) which is the total number of T-shirts, and the number of outcomes that are favorable to us is equal to 18 (outcomes without a black T-shirt). Therefor probability of the chosen T-shirt not being black will be equal to...
18/20 = 9/10