A bag holds 3 red and 2 blue marbles. Two marbles are drawn without replacement. What is the probability that both are red?
Answer and explanation
Correct answer: D. 3/10
- Step 1: The first draw is red with probability 3/5.
- Step 2: Then 2 red remain among 4, so the second is red with probability 2/4.
- Step 3: Multiply: 3/10.
Answer
3/10.
Why not the others: 9/25: the first marble was assumed to be replaced. 7/10: the probabilities were added instead of multiplied. 3/5: only the first draw was considered.
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