Question

A bag contains 10 balls.

4 are red and 6 are blue.
2 balls are taken from the bag at random without replacement.
a) Write down the probability that there are at least 2 red balls still in the bag. (1)
b) Write down the probability that there are at least 3 red balls still in the bag. (3)
Your final line must say, P(at least 3 red) = a/b where a and b are integers.
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Total marks: 4

Answer 1

Explanation:

a) since there are 4 red balls, at least 2 of them will ever remain in the bag

probability = 100% = 1

b) probability that 2 red balls are taken

4/10 x 3/9

2/5 x 1/3

2/15

15/15 - 2/15 = 13/15

P(at least 3 red) = 13/15