How many are not — Percentages Aptitude Question
How many are not: 72% of 25 students are good at mathematics. How many are not good at it? Answer and worked solution on CodeKairo.
- Topic: Percentages
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 35 seconds
Question
72% of 25 students are good at mathematics. How many are not good at it?
Options
- 5
- 6
- 7
- 8
Show the answer and the worked solution
Correct answer: C. 7
Worked solution
- Not good at it = 100% − 72% = 28%.
- 28% of 25 = 7.
Answer: 7.
The idea
Take the complement first when it is the smaller figure — one multiplication instead of a multiplication and a subtraction.
Shortcut. 28% of 25 = 25% of 28 — swapping the percentage and the number turns it into a quarter of 28, which is 7.
Common trap. 6 — rounding 72% to 75%, so 'not good' becomes 25% of 25 ≈ 6; the exact complement is 28%.