Double and add — Aptitude Question
Double and add: 5 : 12 :: 8 : ? Answer and worked solution on CodeKairo.
- Topic: Analogies & Classification
- Section: Logical Reasoning
- Difficulty: Medium
- Time target: 50 seconds
Question
5 : 12 :: 8 : ?
Options
- 16
- 17
- 18
- 20
Show the answer and the worked solution
Correct answer: C. 18
Worked solution
- 12 = 2 × 5 + 2.
- 2 × 8 + 2 = 18.
Answer: 18.
The idea
Try 2n, 2n ± k and 3n − k when the result is a small multiple of the input. Confirm with the numbers you are given.
Shortcut. 12 = 2 × 6 = 2 × (5 + 1), so the rule is 2(n + 1): 2 × 9 = 18.
Common trap. 16 — doubling 8 and dropping the +2 that the given pair (2 × 5 + 2 = 12) requires.
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