Paper 1 · Mathematical Reasoning and Aptitude
UGC NET December 2022 (01.03.2023) Shift-II
What number should replace the question mark in the series given below? 55, 47, 74, 10, 135, -81, 262, ?
A774
B-250 ✓ Correct
C343
D-343
Correct answer: (B) -250 — The missing number is minus 250, so the answer is minus 250.
Explanation
★The missing number is minus 250, so the answer is minus 250.
★The differences between the terms are successive cubes with alternating signs.
★From 55 to 47 the change is minus 8, which is minus 2 cubed, then plus 27, which is 3 cubed.
★Then come minus 64, plus 125, minus 216 and plus 343.
★So the next change is minus 8 cubed, which is minus 512.
★Adding minus 512 to the last term 262 gives minus 250.
★So the missing number is minus 250.
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