CMA Foundation · Fundamentals of Business Mathematics and Statistics · Probability
A bag has 5 red and 3 green balls. Two balls are drawn one after another without replacement. What is the probability that both balls are of the same colour?
The probability of drawing two balls of the same colour is 13/28. Both red has probability 5/8 times 4/7, which is 20/56, and both green is 3/8 times 2/7, which is 6/56. Adding gives 26/56, or 13/28.
- A13/28Correct
- B15/28
- C1/2
- D5/14
Explanation
P(both red) = (5/8)(4/7) = 20/56. P(both green) = (3/8)(2/7) = 6/56. Sum = 26/56 = 13/28. Option 15/28 results from adding unequal wrong terms, and 1/2 is a rough guess.
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