Number Series Interview Questions
Find the next number: 2, 6, 12, 20, 30, ? — spoken sample answer for Indian interviews.
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Find the next number: 2, 6, 12, 20, 30, ?
I look at the gaps: plus 4, plus 6, plus 8, plus 10, so the next gap is plus 12. 30 plus 12 is 42. Another way to see it: 1 times 2, 2 times 3, 3 times 4, 4 times 5, 5 times 6, so the next is 6 times 7 = 42. I would mark 42.
Next: 3, 9, 27, 81, ?
Times 3. Next 243. I state the rule before the number. MCQs put 162 to catch add-81 mistakes.
2, 3, 8, 27, 112, ?
Times n plus n: 2*1+1=3, 3*2+2=8, then 27, 112, next 112*5+5=565. If I cannot see it in 30 seconds I skip on a timed paper.
Odd one out: 8, 27, 64, 100, 125.
Cubes except 100 which is 10 squared. Odd one is 100. I check squares and cubes first on integer lists.
How do you attack a series you do not recognize?
Differences, second differences, multiply factor, plus n, primes, squares. Then mark and move. I do not fit a cubic to four points on NQT. Process beats stubbornness.
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