Out of first 20 natural numbers, one number is selected at random. The probability that it is either an even number or a prime number is_____________?
Correct answer: D. 17/20
- A. 1/2
- B. 16/19
- C. 4/5
- D. 17/20
Explanation
Among 1 to 20, there are 10 even numbers and 8 primes: 2, 3, 5, 7, 11, 13, 17 and 19. Since 2 is counted in both groups, the favourable count is 10 + 8 - 1 = 17, giving 17/20. The likely mistake is choosing 4/5 by incorrectly treating 2 as an overlap to subtract without checking the resulting count, or by counting only 16 favourable numbers.
Last updated
About Ratio and Proportion
Ratios compare quantities in the same units, while proportions state that two ratios are equal. Problems cover simplification, division in a given ratio, direct and inverse variation, scale, and missing terms, with attention to the difference between a ratio and a fraction representing part of a whole.
Practise Arithmetic
1,060 free Arithmetic MCQs from Mathematics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Exams that ask Mathematics questions like this
Mathematics is on 67 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.