Comparing two numbers through a third — Aptitude Question
Comparing two numbers through a third: Two numbers are respectively 20% and 50% more than a third number. Answer and worked solution on CodeKairo.
- Topic: Percentages
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 50 seconds
Question
Two numbers are respectively 20% and 50% more than a third number. The first is what percent of the second?
Options
- 70%
- 75%
- 80%
- 90%
Show the answer and the worked solution
Correct answer: C. 80%
Worked solution
- Let the third number be 100. Then the first is 120 and the second is 150.
- 120/150 = 0.80 = 80%.
Answer: 80%.
The idea
Anchor the quantity everything else is described against at 100. Every comparison then reads straight off without algebra.
Shortcut. The ratio is 1.2 : 1.5 = 4 : 5 = 80%; the third number cancels, so no base needs choosing.
Common trap. 70% — subtracting the 30-point gap (50 − 20) from 100% instead of dividing 120 by 150.