A bag contains 9 green marbles, 5 yellow marbles and 6 red marbles. You choose one marble. What is the probability of selecting a green or red marble?

15/20 or 3/4

Step-by-step explanation:

9 green marbles (GM) + 5 yellow marbles (YM) + 6 red marbles (RM) = 20 marbles total (TM)

GM = 9/20

YM = 5/20

RM = 6/20

TM = 20/20

For the probability of choosing a GM or RM you just add their respective values:

9/20 + 6/20 = 15/20

Simplified this answer is 3/4