A bag contains 10 red marbles, 15 yellow marbles and 5 green marbles. What is the probability of drawing a red or green marble from the bag?

10 (red) plus 5 (green) equals 15. red plus green plus yellow equals 30 15/30 - 50%

Probability =

(number of ways it can come out the way you want)

divided by

(total number of ways it can come out).

Total number of ways to draw a marble = 30 (marbles in the bag).

Number of ways it can succeed = 15 (number of red or green ones)

Probability = 15/30 = 1/2 = 50%.