SSC CGL 2025 Tier-I · 18 September 2025, Shift 2 · General Intelligence and Reasoning · Question 11 of 100

We transcribed this text from the pictures on a candidate's response sheet for this shift; the answer is the key SSC colour-marked on that sheet. Solution last reviewed 11 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. From 2025 the candidate response sheet prints every question and option as a picture, so the text here is transcribed from those pictures for this shift and checked against them independently; where the layout carries meaning, the picture is shown as well. Each answer is the key SSC colour-marked on that sheet. SSC released a tentative key for challenge and later its final one, both only to candidates behind a login, and the sheet does not say which of the two it carries. The solutions are written by UnlockIAS.

What comes at the place of question mark: 2, 6, 12, 20, 30, ?

(a)42
(b)56
(c)38
(d)48

Answer

Why

Correct — A.
Rule: n × (n + 1), so the differences rise +4, +6, +8, +10, +12.

1 × 2 = 2, 2 × 3 = 6, 3 × 4 = 12
4 × 5 = 20, 5 × 6 = 30
Next: 6 × 7 = 42

Check by differences: 30 + 12 = 42 → option (a).

Why the others are wrong

(b)
56 — 56 is 7 × 8, the term after 42. It skips 6 × 7, and the jump 30 → 56 would be +26 instead of +12.
(c)
38 — 38 adds only 8 to 30, repeating an earlier gap. The differences grow by 2 each time, so after +10 comes +12.
(d)
48 — 48 adds 18 to 30. After +10 the next gap is +12, not +18, so 48 overshoots.

Concept

Each term is a number times the next number: 1 × 2, 2 × 3, 3 × 4 and so on. These are the pronic (oblong) numbers, n(n + 1) = n² + n.

The same series reads as a second-difference pattern too. The gaps 4, 6, 8, 10 rise by 2, so the next gap is 12. Either route gives 42, and using both is a free check.

Halve every term and you get 1, 3, 6, 10, 15, 21, the triangular numbers. Doubling 21 gives 42 again.

Key facts

n(n + 1) for n = 1 to 7: 2, 6, 12, 20, 30, 42, 56.
Each pronic number is twice a triangular number: 42 = 2 × 21.
Consecutive pronic numbers differ by 2(n + 1): 30 to 42 is 2 × 6 = 12.

Study next

Series built on n² + 1, n² − 1 and n³Wrong-term items on a product seriesSeries whose differences form a series of their own

Common traps

Picking 56 by jumping to 7 × 8 and skipping 6 × 7
Repeating an earlier gap instead of letting the gaps keep rising by 2

15 Sep 2025, 16:00, Reasoning Q.18 prints the same series, 2, 6, 12, 20, 30, ?, keyed 42 (option b).

Related PYQs

No directly related past PYQ was found.

Topic: Number Series — all 112 SSC CGL questions on it, every solved shift.