Exams › IBPS PO › Quantitative Aptitude
Two boxes contain 4 and 16 balls respectively. Two balls in the first box and four in the second box are black. If a box is chosen at random and two balls are drawn at random from it without replacement, what is the probability that at least one ball is black?
- None of these
- -3
- 20
- None of these
Correct answer: None of these
Solution
The probability of at least one black ball is easier to find using the complement: 1 minus the probability that both drawn balls are non-black. For the 4-ball box, there are 2 black and 2 non-black balls, so drawing two non-black balls is impossible. For the 16-ball box, the probability can be computed, and the final value does not match the listed numeric options, so the correct choice is None of these.
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