CA Foundation · Quantitative Aptitude · Probability
A number is chosen at random from the integers 1 to 60. What is the probability that it is divisible by 4 or by 6 but not by both?
The probability is 1/4. There are 15 multiples of 4, 10 of 6 and 5 of 12 up to 60. Excluding the common multiples, 10 plus 5 gives 15 favourable numbers out of 60, so 15/60 equals 1/4.
- A1/4
- B1/3
- C7/30Correct
- D4/15
Explanation
Divisible by 4: 15. By 6: 10. By both means by 12: 5. Exactly one: (15-5)+(10-5)=15. Probability = 15/60 = 1/4. Check: 'or' including both gives 20/60=1/3, which is wrong as it includes multiples of 12.
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