Probability =
(number of ways to be successful)
divided by
(total number of things that can happen) .
There are 50 pencils in the bag all together, of all colors.
Total number of things that can happen = 50 .
You get a freebie if you pull a red or a green from the bag.
There are 5 reds in the bag.
There are 10 greens in the bag.
Number of ways to be successful = (5 + 10) = 15 .
Probability = (15) / (50) = 3/10 = 30 % .