Problem-Solving and Data AnalysisHardProbability that two draws are not both red
Problem-Solving and Data Analysis practice question
A box holds 3 red and 2 blue pens. Two pens are taken out at random without replacement. What is the probability that the two pens are not both red?
Answer: 7/10 or 0.7
P(both red) = 3/5 × 2/4 = 3/10, so P(not both red) = 7/10.
Common wrong answers
- If you answered 3/10
- 3/10 is the probability that both are red.
- If you answered 16/25
- 16/25 treats the draws as with replacement.
- If you answered 2/5
- 2/5 is the probability that the first pen is blue.
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