Divisible by 5 — Probability Aptitude Question
Divisible by 5: A number is chosen at random from 1 to 50. What is the probability that it is divisible by 5? Answer and worked solution on CodeKairo.
- Topic: Probability
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 45 seconds
Question
A number is chosen at random from 1 to 50. What is the probability that it is divisible by 5?
Options
- 1/10
- 1/5
- 1/4
- 3/10
Show the answer and the worked solution
Correct answer: B. 1/5
Worked solution
- Multiples of 5 from 1 to 50: 10 numbers.
- Probability = 10/50 = 1/5.
Answer: 1/5.
The idea
Count the favourable cases with ⌊n/d⌋ and divide by the range size. No listing is needed once the count is clear.
Shortcut. One number in every five is a multiple of 5, and 1 to 50 is a whole number of fives, so the probability is exactly 1/5 with no counting.
Common trap. "1/10" — writing 5/50 by putting the divisor 5 on top instead of the count of multiples, which is 50 ÷ 5 = 10.