7, 26, 63, 124, ? — Number & Letter Series Aptitude Question
7, 26, 63, 124, ?: Find the next term: 7, 26, 63, 124, ? Answer and worked solution on CodeKairo.
- Topic: Number & Letter Series
- Section: Logical Reasoning
- Difficulty: Medium
- Time target: 60 seconds
Question
Find the next term:
7, 26, 63, 124, ?
Options
- 180
- 195
- 215
- 216
Show the answer and the worked solution
Correct answer: C. 215
Worked solution
- Adding one gives 8, 27, 64, 125 — that is 2³, 3³, 4³, 5³.
- Next term = 6³ − 1 = 216 − 1 = 215.
Answer: 215.
The idea
Offsetting by one is the standard disguise for a cube series. Note the trap of choosing 216 itself.
Shortcut. The gaps 19, 37, 61 rise by 18 then 24, so the next rise is 30: gap 91, and 124 + 91 = 215. Units check: 6³ ends in 6, so 6³ − 1 ends in 5.
Common trap. 216 — spotting 6³ and forgetting to subtract the 1 that every term carries (8 − 1, 27 − 1, …).