PROBABILITY C10

A bag contains 10 red pencils and 7 blue pencils. Two pencils  are taken from the bag. What is the probability that they are both blue?

Solution

(This is a problem with replacement)

n(R) = 10, n(B) = 7, n(S) = 18

P(B) = n(B)

           n(S)

1st pick = 7/18

2nd pick = 7/18 as well.

P(B) =  7      x    7

           18          18

P(B) =    49    

             324         

Therefore Probability of drawing a blue pencil is 49/324     


TRY THIS..........

 A bag contains 6 red pencils and 10 blue pencils. Two pencils  are taken from the bag. What is the probability that they are both red?