SSC CGL 2025 Tier-I · 15 September 2025, Shift 3 · General Intelligence and Reasoning · Question 18 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 next in the series: 2, 6, 12, 20, 30, ?

(a)40
(b)42
(c)44
(d)36

Answer

Why

Correct — B.
Rule: differences +4, +6, +8, +10, each 2 more than the last.

2 → 6 (+4)
6 → 12 (+6)
12 → 20 (+8)
20 → 30 (+10)

Next difference: +12
30 + 12 = 42 → option (b).

Why the others are wrong

(a)
40 — 40 adds 10 again, repeating the last difference. The differences climb by 2 each time, so the next one is 12.
(c)
44 — 44 adds 14, skipping the +12 step. It also fails the product check: the sixth term is 6 × 7 = 42.
(d)
36 — 36 adds only 6, breaking the rising differences. It is 6², the square, where the series needs 6 × 7.

Concept

When the gaps between terms form their own simple sequence, look at the second difference. Here the gaps 4, 6, 8, 10 rise by a constant 2.

The same terms are products of two consecutive numbers, n(n + 1): 1×2, 2×3, 3×4, 4×5, 5×6. The next is 6×7 = 42, so the two readings confirm each other.

Key facts

n(n + 1) for n = 1 to 7: 2, 6, 12, 20, 30, 42, 56.
The gap between n(n + 1) and the next such product is 2(n + 1): 4, 6, 8, 10, 12.
A constant second difference marks a quadratic series.

Study next

Series built on n² + 1, n² − 1 and n³ − nSeries whose differences form a geometric progressionWrong-term questions inside a quadratic series

Common traps

Repeating the last difference (+10) and choosing 40
Confusing n(n + 1) with n², which gives 36

18 Sep 2025, 12:30, Reasoning Q.11 prints the same series, 2, 6, 12, 20, 30, keyed 42. 12 Sep 2025, 16:00, Reasoning Q.3 uses 3×4, 5×6 and onward (12, 30, 56, 90, 132), keyed 182 = 13×14.

Reasoning Q.8 of this shift also runs on rising differences: 14, 17, 20, 23.

Related PYQs

No directly related past PYQ was found.

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