One person replaced — Averages Aptitude Question
One person replaced: The average weight of 8 people increases by 2.5 kg when a person weighing 65 kg is replaced by… Answer and worked solution on CodeKairo.
- Topic: Averages
- Section: Quantitative Aptitude
- Difficulty: Easy
- Time target: 45 seconds
Question
The average weight of 8 people increases by 2.5 kg when a person weighing 65 kg is replaced by a new one. What is the new person's weight?
Options
- 75 kg
- 80 kg
- 85 kg
- 90 kg
Show the answer and the worked solution
Correct answer: C. 85 kg
Worked solution
- Rise in total weight = 8 × 2.5 = 20 kg.
- New person = 65 + 20 = 85 kg.
Answer: 85 kg.
The idea
When one member is swapped, the change in total equals n × (change in average). Add that to the outgoing member's value.
Shortcut. Test by difference: (85 − 65) ÷ 8 = 2.5 exactly, while 80 and 90 give 1.875 and 3.125.
Common trap. 90 kg — adding 25 to 65 (2.5 read as 25, or multiplied by 10 rather than by the 8 people).