CA Foundation · Quantitative Aptitude · Probability
A box contains 20 tickets numbered 1 to 20. One ticket is drawn at random. What is the probability that the number is a multiple of 3 or a multiple of 5?
The probability is 9/20. There are 6 multiples of 3 and 4 multiples of 5 among the numbers 1 to 20, and 15 is counted in both. So favourable outcomes are 6 + 4 - 1 = 9 out of 20.
- A9/20Correct
- B2/5
- C1/2
- D11/20
Explanation
Multiples of 3: 3,6,9,12,15,18 gives 6. Multiples of 5: 5,10,15,20 gives 4. Common: 15 gives 1. Favourable = 6 + 4 - 1 = 9, so probability = 9/20. Option 10/20 would ignore the overlap.
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