SSC CGL 2025 Tier-I · 18 September 2025, Shift 1 · General Intelligence and Reasoning · Question 5 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 13 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: 1, 2, 6, 24, 120, ?

(a)720
(b)504
(c)840
(d)600

Answer

Why

Correct — A.
Rule: multiply by 2, 3, 4, 5, 6, each term being the last one times the next whole number.

1 × 2 = 2
2 × 3 = 6
6 × 4 = 24
24 × 5 = 120

120 × 6 = 720 → option (a).

Why the others are wrong

(b)
504 — 504 is 120 × 4.2. Every step so far multiplies by a whole number one larger than the last, so after × 5 comes × 6.
(c)
840 — 840 is 120 × 7. It skips a multiplier: the steps run × 2, × 3, × 4, × 5, so the next is × 6, not × 7.
(d)
600 — 600 is 120 × 5, repeating the last multiplier. The multiplier grows by one each step, so the next is × 6.

Concept

These are factorials: n! is 1 × 2 × 3 × … × n. So 2! = 2, 3! = 6, 4! = 24, 5! = 120 and 6! = 720.

When the terms grow fast, divide each by the one before instead of subtracting. A ratio pattern shows up at once where differences stay muddy.

Subtracting gives 1, 4, 18, 96, which shows no clear rule.

Dividing gives 2, 3, 4, 5, and the next ratio, 6, follows.

Key facts

1! = 1, 2! = 2, 3! = 6, 4! = 24, 5! = 120, 6! = 720, 7! = 5040.
n! = n × (n − 1)!, so each factorial is the previous one times the next whole number.

Study next

Series where the multiplier alternates, such as × 2, × 3, × 2, × 3Series that combine multiplication and addition, such as × 2 + 1Wrong-number questions built on factorials

Common traps

Repeating the last multiplier (× 5) and choosing 600
Hunting for a pattern in the differences, which grow without a clear rule

21 Sep 2025, 16:00, Reasoning Q.6 prints the factorials backwards, 5040, 720, 120, 24, 4, 2, and keys 4 as the wrong number, since 3! is 6.

Related PYQs

No directly related past PYQ was found.

Topic: Number Series — all 178 SSC CGL questions on it, every solved shift.