SSC CGL 2024 Tier-I · 12 September 2024, Shift 3 · General Intelligence and Reasoning · Question 18 of 100

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 6 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.

Select the option that represents the letters which, when sequentially placed from left to right in the blanks below, will complete the letter series. f d _ e _ e f _ d d _ d _ f f _ d _ d _ f

(a)d d f e e d e d
(b)d d f e f d e e
(c)d d f d e d e f
(d)d d f e e d e e

Answer

Why

Correct — D. Number the places before you touch the options.

Rule: the string is one 7-letter unit, f d d e d e f, laid down three times over 21 places.

Places 1–7: f d d e d e f
Places 8–14: f d d e d e f
Places 15–21: f d d e d e f

The eight blanks sit at places 3, 5, 8, 11, 13, 16, 18 and 20, and the repeating unit fills them with d, d, f, e, e, d, e, e — option (d).

Why the others are wrong

(a)
d d f e e d e d — Option (a) is right for seven blanks and then puts d at place 20, where the third pass through the unit needs e. One wrong letter is enough, so check the last blank as carefully as the first.
(b)
d d f e f d e e — Option (b) puts f at place 13. That is the sixth letter of the second pass, which must be e, so the middle seven letters stop matching the seven either side of them.
(c)
d d f d e d e f — Option (c) breaks two places — d at place 11 and f at place 20 — both of which the repeating unit fills with e.

Concept

A missing-letter series is a repeating unit with holes punched in it. The work is finding the length of that unit, not guessing letters one blank at a time.

Count the places first. Twenty-one places factorise as 3 × 7, which points straight at a seven-letter unit laid down three times, and the visible letters then confirm it.

Once the unit is known every blank is fixed by its position, and there is nothing left to judge — which is why this question type is worth attempting in full.

Every option opens with the same three letters, d d f, so the first three blanks separate nothing. The question is decided entirely in the last five.

Key facts

The completed series is f d d e d e f, repeated three times over 21 places.
The eight blanks fall at places 3, 5, 8, 11, 13, 16, 18 and 20.
Factorising the total length is the fastest route in — 21 places suggest a 7-letter unit taken three times.

Study next

Repeating-unit letter series where the unit length must be deduced from the total countSeries that repeat a unit with one deliberate substitution each cycleAlphabet-shift series in which each letter position carries its own step

Common traps

Filling blanks left to right by feel without ever writing the block out.
Checking the early blanks, finding a match and never testing the last one, which is how option (a) collects marks.

Letter series also runs at 12 Sep 2024, 16:00, Reasoning Q.5, there as four clusters in which each letter position carries its own shift rather than as one repeating block.

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