Logical reasoning · Day 11
Odd One Out / Classification
Find the rule that three share. The odd one breaks it. Check primes, squares, cubes, even/odd, vowels, letter gaps.
Why this topic matters
Apple, mango, carrot, banana: carrot is the odd one because it is a vegetable. Find the rule three of them share.
Classification is quick marks: find a property that three options share and one does not.
Numbers and letters
Numbers: test prime or not, square or cube, even or odd, digit sum, divisible by something.
Letters: convert to positions and test gaps, vowels, opposite pairs.
Example 1Find the odd one: 27, 64, 125, 144, 216
- 27 = 33, 64 = 43, 125 = 53, 216 = 63.Cubes.
- 144 = 122 is not a cube.
Answer: 144
Example 2Find the odd one: BD, FH, JL, NQ
- BD: gap 2. FH: 2. JL: 2. NQ: 3.Letter positions.
- NQ.
Answer: NQ
Formula summary
Numbers
Prime / composite, square / cube, divisible by, digit sum.
Letters
Gaps between letters, vowels, reverse pairs.
Words
Category (fruit, tool), function, part-whole.
Shortcuts and tricks
Letter-gap check
Use it when: Letter groups.
- Convert to positions and look at the gaps.
ExampleACE, BDF, GIK, LNQ
- Gaps 2,2 in the first three; LNQ is 2,3.
Answer: LNQ
Before you move on, you should be able to...
- test prime, square, cube, parity and digit sum
- turn letters into positions and compare gaps
Practice questions (5)
Try each one before opening the solution. Or practise them one by one so your score is saved.
easy Odd one: 2, 3, 5, 9, 11
- Only non-prime.
Answer: 9
easy Odd one: 16, 25, 36, 48, 64
- Not a perfect square.
Answer: 48
easy Odd one: Apple, Mango, Potato, Banana
- Vegetable.
Answer: Potato
easy Odd one: 8, 27, 64, 100, 125
- Only non-cube.
Answer: 100
medium Odd one: AZ, BY, CX, DV
- Reverse pairs sum to 27: D(4)+W(23). DV is 4+22.
Answer: DV
Class plan (2 hours, for trainers)
A tested order for teaching this topic in one 2-hour session. Present mode follows the same order.
| 10 min | Warm-up. |
| 35 min | Number properties checklist. |
| 30 min | Letter groups by position. |
| 40 min | Practice set. |
| 5 min | Recap. |