Paper 1 · Mathematical Reasoning and Aptitude
UGC NET December 2023 (12.12.2023) Shift-I
What number would replace the question mark (?) in the series given below? 1, 3, 6, 10, 15, 21, ?, 36
A32
B28 ✓ Correct
C29
D30
Correct answer: (B) 28 — The missing number is 28, so that is the answer.
Explanation
★The missing number is 28, so that is the answer.
★These are the triangular numbers, formed by adding successive natural numbers.
★Each term adds the next counting number to the previous term.
★After 21 the next number added is 7, giving 21 plus 7.
★That equals 28, and adding 8 to 28 gives 36, which fits the next term.
★So the missing number is 28.
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