CA Foundation · Quantitative Aptitude · Probability
A box has 4 red and 6 black balls. Two balls are drawn at random without replacement. What is the probability that both balls have the same colour?
The probability is 7/15. Total ways to pick two balls are 45. Two red balls can be chosen in 6 ways and two black balls in 15 ways, giving 21 favourable ways. Hence 21/45 simplifies to 7/15.
- A7/15Correct
- B8/15
- C1/2
- D2/5
Explanation
Total ways = C(10,2) = 45. Both red: C(4,2) = 6. Both black: C(6,2) = 15. Favourable = 21, so probability = 21/45 = 7/15. Option 8/15 is the probability of different colours (24/45).
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