A bag holds 6 red and 4 blue beads. Two beads are drawn one after the other without replacement. What is the probability that both are red?
Answer and explanation
Correct answer: D. 1/3
- Step 1: P(first red) = 6/10. Step 2. After one red is removed, P(second red) = 5/9. Step 3. Multiply: 6/10 x 5/9 = 1/3. Answer: 1/3. Why not the others: 9/25: That would be true only if the first bead were put back. 2/5: That forgets that one red bead has already been removed, so only 5 red remain. 52/45: Probabilities of successive events are multiplied, not added.
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