SSC CGL 2025 Tier-I · 19 September 2025, Shift 1 · General Intelligence and Reasoning · Question 24 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 next number in the series : 2, 5, 11, 23, 47, ?

(a)95
(b)97
(c)93
(d)99

Answer

Why

Correct — A.
Rule: each term = previous × 2 + 1.

2 × 2 + 1 = 5
5 × 2 + 1 = 11
11 × 2 + 1 = 23
23 × 2 + 1 = 47

Next: 47 × 2 + 1 = 95 → option (a).

Why the others are wrong

(b)
97 — 97 is 47 × 2 + 3. Every earlier step adds exactly 1 after doubling, so the next term is 95.
(c)
93 — 93 is 47 × 2 − 1, a gap of 46. The gaps 3, 6, 12, 24 double, so the next gap is 48.
(d)
99 — 99 is 47 × 2 + 5, a gap of 52. The gaps double each time, so after 24 comes 48, not 52.

Concept

When the gaps in a series double (3, 6, 12, 24), look for a multiply-then-add rule. Here each term is the previous one × 2 + 1.

The two views agree: 47 × 2 + 1 = 95, and 47 + 48 = 95, since the next gap doubles 24 to 48.

A third check: add 1 to each term and you get 3, 6, 12, 24, 48, a clean doubling. The next is 96, and 96 − 1 = 95.

Key facts

Any '× 2 + c' rule makes the gaps double, whatever c is.
Here the gaps run 3, 6, 12, 24, 48.
Each term here is one less than 3 × a power of 2: 3, 6, 12, 24, 48, 96 minus 1.

Study next

× 3 + c and × 2 − c seriesSeries that alternate two operations (× 2, then + 3)Finding a missing middle term in a multiply-add series

Common traps

Seeing the doubling gaps but adding the old gap: 47 + 24 = 71
Doubling 47 and stopping at 94 without the + 1

17 Sep 2025, 16:00, Reasoning Q.24 runs the same × 2 + 1 rule from 3: 3, 7, 15, 31, 63, keyed 127.

Reasoning Q.12 in this shift uses × 2 − 1 instead: 2, 3, 5, 9, 17, 33, keyed 65.

Related PYQs

No directly related past PYQ was found.

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