PROBABILITY K3

 

A bag contains 13 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) = 13, n(B) = 7, n(S) = 20

 

P(B) = n(B)

           n(S)

 

1st pick = 7/20

2nd pick = 7/20 as well.

 

 

P(B) =  7      x    7

           20          20

 

P(B) =    49    

             400         

 

Therefore Probability of drawing a blue pencil is 49/400     


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

 A bag contains 6 red pencils and 8 yellow pencils. Two pencils are taken from the bag. What is the probability that they are both red?