SSC CGL 2025 Tier-I · 18 September 2025, Shift 2 · General Intelligence and Reasoning · Question 6 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.

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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.

Find the WRONG term in the given series. 5, 10, 15, 26, 37, 50

(a)50
(b)26
(c)15
(d)5

Answer

Why

Correct — C.
Rule: n² + 1 for n = 2, 3, 4, 5, 6, 7.

2² + 1 = 5 ✓ and 3² + 1 = 10 ✓
4² + 1 = 17, but the series prints 15 ✗
5² + 1 = 26 ✓, 6² + 1 = 37 ✓, 7² + 1 = 50 ✓

Check: with 17 the differences run +5, +7, +9, +11, +13.
15 is the wrong term → option (c).

Why the others are wrong

(a)
50 — 50 is 7² + 1, and 37 + 13 = 50 keeps the odd differences going. It fits the rule.
(b)
26 — 26 is 5² + 1. From 17 it is +9 and on to 37 it is +11, so it sits in the odd-difference run.
(d)
5 — 5 is 2² + 1, the first term of the rule. The gap to 10, +5, starts the run of odd differences.

Concept

A wrong-term item hides one bad number in a rule-based series. Find a rule most terms obey, then find the term that breaks it.

Here each term is one more than a square: 5, 10, 17, 26, 37, 50 are 2², 3², 4², 5², 6², 7² plus 1. Consecutive squares differ by the odd numbers, so the gaps grow +5, +7, +9, +11, +13.

The printed gaps are +5, +5, +11, +11, +13. One wrong term spoils two neighbouring gaps: 10 → 15 and 15 → 26 are both off, and 15 sits between them. That is the fastest way to spot it.

Key facts

Squares 1 to 10: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100.
Consecutive squares differ by consecutive odd numbers: 4, 9, 16 differ by 5 and 7.
A single wrong term breaks the two differences on either side of it.

Study next

Wrong-term series built on n² − 1 or n³ + 1Series whose differences themselves form a seriesMissing-term series built on n(n + 1)

Common traps

Reading 5, 10, 15 as a +5 table and passing 15 as correct
Blaming 26 because the gap 15 → 26 looks too big, when 15 is the term that broke both gaps

19 Sep 2025, 09:00, Reasoning Q.6 hides one wrong term the same way: 336, 246, 166, 94, 36, −14 should fall by 90, 80, 70, 60, 50, so 94 should be 96 (keyed a).

Related PYQs

No directly related past PYQ was found.

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