Average of the first five multiples of 3 — Aptitude Question
Average of the first five multiples of 3: What is the average of the first five multiples of 3? Answer and worked solution on CodeKairo.
- Topic: Averages
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 35 seconds
Question
What is the average of the first five multiples of 3?
Options
- 6
- 9
- 12
- 15
Show the answer and the worked solution
Correct answer: B. 9
Worked solution
- The multiples are 3, 6, 9, 12, 15.
- With an odd count of evenly spaced terms the average is the middle term: 9.
Answer: 9.
The idea
An odd number of evenly spaced terms has its average sitting exactly on the middle term. No addition is needed at all.
Shortcut. The first n multiples of k average k(n + 1)/2 = 3 × 6/2 = 9.
Common trap. "6" — counting 0 as the first multiple, so the list becomes 0, 3, 6, 9, 12.