SSC CGL 2024 Tier-I · 11 September 2024, Shift 1 · General Intelligence and Reasoning · Question 11 of 95

Text as printed on a candidate's response sheet for this shift; answer per SSC's tentative key as marked on that sheet. Solution last reviewed 10 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. The questions and options here are reproduced as printed on a candidate's own response sheet for this shift — the Commission's text, unchanged. Each answer is SSC's tentative key as marked on that sheet; SSC allowed challenges to it and never publishes a final key. The solutions are written by UnlockIAS.

Which of the following numbers will replace the question mark (?) in the given series? 17, 38, 84, ?, 376, 772

(a)150
(b)190
(c)180
(d)200

Answer

Why

Correct — C. Rule: double the previous term, then add 4, 8, 12, 16, 20 — the addition grows by 4 at every step.

17 × 2 + 4 = 38
38 × 2 + 8 = 84
84 × 2 + 12 = 180

180 × 2 + 16 = 376
376 × 2 + 20 = 772

The blank is 180, option (c), and it is the value that carries the series through to both 376 and 772.

Why the others are wrong

(a)
150 — 150 doubles to 300, and reaching 376 from there needs +76 where the run calls for +16. It also breaks the step before it, since 84 × 2 + 12 is 180.
(b)
190 — 190 doubles to 380, which is already past 376. Every addition in this series is positive, so any term above 180 overshoots the next given number.
(d)
200 — 200 doubles to 400 and would need 24 subtracted to reach 376. Nothing in the series subtracts.

Concept

When a series roughly doubles, test ×2 plus something before anything else. Double each term, subtract the result from the next term, and read the remainders.

Here the remainders are 4, 8, 12, 16, 20 — an arithmetic run rising by 4. The two steps before the blank establish it, and the two steps after it confirm it.

The same series also reads through its differences: 21, 46, 96, 196, 396, where each difference is twice the one before it plus 4. Either reading lands on 180.

Only 376 can settle the blank. Working forward gives a candidate, but the check that matters is whether that candidate doubled plus 16 reaches 376 — and only 180 does.

Key facts

17 × 2 + 4 = 38, 38 × 2 + 8 = 84 and 84 × 2 + 12 = 180.
The additions across this series are 4, 8, 12, 16 and 20, rising by 4 each time.
180 × 2 + 16 = 376 and 376 × 2 + 20 = 772, which closes the series.

Study next

Series of the form previous × n + constant, where the multiplier changes instead of the additionDifference-of-differences series, where the second differences are constantWorking a series backwards from a later known term to fix a blank

Common traps

Fixing on a constant +4 after the first step, which gives 80 instead of 84 at the third term
Solving forward only and never testing the answer against 376
Reading 376 and 772 as an exact doubling, which is off by 20

The same doubling shape also runs at 11 Sep 2024, 16:00, Reasoning Q.20 with 12, 25, 49, ?, 197, 395, and at 9 Sep 2024, 9:00, Reasoning Q.25 with 1, 3, 10, 41, ?, 1237, where it is the multiplier that changes at every step rather than the addition.

Related PYQs

No directly related past PYQ was found.