CA Foundation · Quantitative Aptitude · Probability
A box contains 6 good and 4 defective pens. Three pens are picked at random together. What is the probability that exactly one pen is defective?
The probability is 1/2. Of the 120 ways to pick three pens from ten, 60 ways give one defective pen (4 choices times 15 pairs of good pens), so the probability is 60/120, which equals one half.
- A1/2Correct
- B3/10
- C1/3
- D2/5
Explanation
Total ways = 10C3 = 120. Exactly one defective = 4C1 × 6C2 = 4 × 15 = 60. Probability = 60/120 = 1/2. Using 6C3 × 4 wrongly or ignoring combinations gives other values.
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