The fourth proportional — Aptitude Question
The fourth proportional: What is the fourth proportional to 4, 6 and 10? Answer and worked solution on CodeKairo.
- Topic: Ratio & Proportion
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 40 seconds
Question
What is the fourth proportional to 4, 6 and 10?
Options
- 12
- 14
- 15
- 16
Show the answer and the worked solution
Correct answer: C. 15
Worked solution
- 4 : 6 = 10 : x means 4x = 6 × 10 = 60.
- x = 15.
Answer: 15.
The idea
Fourth proportional to a, b, c is bc/a. Third proportional to a, b is b²/a. Mean proportional between a and b is √(ab).
Shortcut. 6 is 1.5 times 4, so the fourth term is 1.5 times 10 = 15.
Common trap. 12 — adding the difference (10 + 2) instead of keeping the ratio; proportion means equal ratios, not equal gaps.