If a box contains 3 red pens and 7 black pens, two pens are drawn one after another without replacement. What is the probability that both pens drawn are red?
Answer and explanation
Correct answer: B. 1/15
- Step 1: Probability of first pen being red: 3/10.
- Step 2: Given the first pen was red, 2 red pens remain out of 9 total pens: 2/9.
- Step 3: Multiply probabilities: P = (3/10) * (2/9) = 6/90 = 1/15.
Answer
1/15.
Why not the others: Option 9/100 draws with replacement (3/10 * 3/10). Option 3/10 is the probability of only the first draw. Option 1/10 computes 2/20.
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