The students are selling school pencils. if a red or green pencil is pulled from a bag, it is free. the bag contains:

5 red
10 green
15 yellow
20 blue

what is the probability that the first buyer will get a free pencil when randomly drawing one from the bag?

a. 3/10
b. 1/10
c. 2/5
d. 1/5

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 % . 

He will need 2,898 pieces of paper