Books in a library — Caselets Aptitude Question
Books in a library: A library holds 5,000 books. 40% are fiction, 35% are non-fiction, and the rest are reference. Answer and worked solution on CodeKairo.
- Topic: Caselets
- Section: Data Interpretation
- Difficulty: Medium
- Time target: 90 seconds
Question
A library holds 5,000 books. 40% are fiction, 35% are non-fiction, and the rest are reference. During a year, 10% of the fiction and 20% of the reference books are borrowed at least once.
How many books were borrowed at least once?
Options
- 350
- 450
- 500
- 550
Show the answer and the worked solution
Correct answer: B. 450
Worked solution
- Fiction = 40% of 5,000 = 2,000. Reference = 100% − 40% − 35% = 25% of 5,000 = 1,250.
- Borrowed fiction = 10% of 2,000 = 200.
- Borrowed reference = 20% of 1,250 = 250.
- Non-fiction is never borrowed in this caselet, so the total is 200 + 250 = 450.
Answer: 450.
The idea
Compute the missing category from the percentages that are given, then apply each rate only to the category it belongs to. The category the question stays silent about is usually the trap.
Shortcut. Work in shares of the whole library: 10% of 40% = 4% and 20% of 25% = 5%, so 9% of 5,000 = 450.
Common trap. 550 comes from applying the 20% to non-fiction (1,750, giving 350) instead of reference: 200 + 350 = 550.