SSC CGL 2025 Tier-I · 18 September 2025, Shift 2 · General Intelligence and Reasoning · Question 25 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.

The series given below contains a sequence of numbers. Accordingly identify the incorrect combination 6, 7, 16, 51, 210

(a)210
(b)16
(c)7
(d)51

Answer

Why

Correct — A.
Rule: × 1 + 1, × 2 + 2, × 3 + 3, × 4 + 4.

6 × 1 + 1 = 7 ✓
7 × 2 + 2 = 16 ✓
16 × 3 + 3 = 51 ✓
51 × 4 + 4 = 208, not 210

So 210 is the incorrect term → option (a).

Why the others are wrong

(b)
16 — 16 = 7 × 2 + 2, the second step of the rule. It fits, and the step after it (16 × 3 + 3 = 51) fits too.
(c)
7 — 7 = 6 × 1 + 1, the rule's first step. Nothing is wrong with it.
(d)
51 — 51 = 16 × 3 + 3 fits. Keep 210 instead and the term before it would have to be (210 − 4) ÷ 4 = 51.5, not a whole number.

Concept

In a wrong-term item, find the rule that most terms obey, then locate the term that breaks it.

Here the multiplier and the number added rise together: × 1 + 1, × 2 + 2, × 3 + 3. The next step is × 4 + 4, so 51 should lead to 208. The series prints 210, two too many.

× n + n is the same as (previous term + 1) × n: (6 + 1) × 1 = 7, (7 + 1) × 2 = 16, (16 + 1) × 3 = 51, (51 + 1) × 4 = 208.

Key facts

Steps here: × 1 + 1, × 2 + 2, × 3 + 3, × 4 + 4.
× n + n equals (term + 1) × n.
The fifth term should be 208.

Study next

Wrong-term series whose gaps doubleSeries with two wrong terms, answered as a pairGrowing-multiplier series without the added number (× 1, × 2, × 3)

Common traps

Blaming 51 because the step after it is off, when the step into it (16 × 3 + 3) fits

17 Sep 2025, 16:00, Reasoning Q.25 uses the same wording on 25, 29, 37, 53, 87: the gaps double (4, 8, 16, 32), so 85 is due and 87 is keyed.

19 Sep 2025, 09:00, Reasoning Q.25 hides two wrong terms in a × 4 series (3, 12, 48, 194, 768, 3074) and keys the pair 194, 3074.

Related PYQs

No directly related past PYQ was found.

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