Consider the sequence
ABC_ _ ABC_ DABBCD_ ABCD
that follows a certain pattern.
Which one of the following completes the sequence?
Answer & explanation
Answer: (d) DDCA
With the blanks filled as D, D, C, A the series splits into groups of five: ABCDD, ABCCD, ABBCD, AABCD. Each group is ABCD with one letter doubled, and the doubled letter moves back from D to C to B to A.
- There are 16 printed letters and 4 blanks: 20 letters, which suggests four groups of five.
- The unbroken stretch DABBCD contains ABBCD — the block ABCD with B doubled.
- So the groups should be ABCD with one letter doubled: ABCDD, ABCCD, ABBCD, AABCD (D, C, B, A doubled in turn).
- Fill the blanks to match: ABC(D)(D) ABC(C) DABBCD(A) ABCD, i.e. D, D, C, A.
- Check: ABCDDABCCDABBCDAABCD splits exactly into ABCDD | ABCCD | ABBCD | AABCD.
Remember · In letter series, count the total letters and try equal groups (4, 5, 6); the stretch without blanks usually shows the rule.
Question and answer: UPSC's official GS Paper II (2023, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·