PROBABILITY 3

A jar contains 10 blue balls and 11 red balls. Two balls are drawn without replacement. What is the probability of getting two red balls?

Solution

Total number of balls = 10 + 11 = 21

Let P(A) = Probability of getting first red ball and
      P(B) = Probability of getting second red ball

Therefore:

P(A) = 11/21

After first withdraw we are left with 20 balls.

So P(B) = 10/20

Probability of 2 red balls = P(A) x P(B)

                                            = 11/21 × 10/20
                                            = 110/420

                                            = 11/42

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

A jar contains 4 green balls and 8 red balls. Two balls are drawn without replacement. What is the probability of getting two green balls?