Third proportional to 4 and 12 — Aptitude Question
Third proportional to 4 and 12: What is the third proportional to 4 and 12? Answer and worked solution on CodeKairo.
- Topic: Ratio & Proportion
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 40 seconds
Question
What is the third proportional to 4 and 12?
Options
- 16
- 24
- 36
- 48
Show the answer and the worked solution
Correct answer: C. 36
Worked solution
- 4 : 12 = 12 : x → 4x = 144.
- x = 36.
Answer: 36.
The idea
Third proportional to a and b is b²/a — the middle term is repeated. Mean proportional between a and b is √(ab), which is a different question.
Shortcut. 12 is 3 × 4, so the next term of the proportion 4, 12, x is 3 × 12 = 36.
Common trap. "48" — multiplying 4 × 12, the first step of the mean proportional √(ab), instead of 12² ÷ 4.