CA Foundation · Quantitative Aptitude · Probability
A box contains 6 white and 4 black balls. Two balls are drawn one after another without replacement. What is the probability that the first is white and the second is black?
The probability is 4/15. By the multiplication theorem, the chance of a white first ball is 6/10 and the chance of a black second ball given that is 4/9, so the product is 24/90, which simplifies to 4/15.
- A4/15Correct
- B6/25
- C2/5
- D1/3
Explanation
P(first white) = 6/10. Given this, 4 black balls remain among 9, so P(second black | first white) = 4/9. The product is 24/90 = 4/15. The value 6/25 comes from (6/10)(4/10), which wrongly assumes replacement.
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