Increasing the side of a square — Aptitude Question
Increasing the side of a square: If the side of a square is increased by 20%, by what percent does its area increase? Answer and worked solution on CodeKairo.
- Topic: Mensuration
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 50 seconds
Question
If the side of a square is increased by 20%, by what percent does its area increase?
Options
- 20%
- 40%
- 44%
- 48%
Show the answer and the worked solution
Correct answer: C. 44%
Worked solution
- New side = 1.2 × old, so new area = 1.2² = 1.44 times the old.
- Increase = 44%.
Answer: 44%.
The idea
Lengths scale by k, areas by k² and volumes by k³. Doubling the percentage (40%) is the standard mistake.
Shortcut. Successive-change rule: 20 + 20 + (20 × 20)/100 = 44%.
Common trap. 40% — doubling the 20% as though area grew in step with the side; the extra 4% is the corner piece 0.2 × 0.2.