Select the letter-cluster from among the given options that can replace the question mark (?) in the following series: PCHJ, PGPV, PKXH, POFT, ?

Correct — A.
Rule: first letter fixed at P; the others step +4, +8, +12.

2nd: C, G, K, O → O(15) + 4 = S(19).
3rd: H, P, X, F → F(6) + 8 = N(14).
4th: J, V, H, T → T(20) + 12 = 32, past Z to F(6).

That gives PSNF → option (a).

Why the others are wrong

• (b)
  PRPG — PRPG fails at the second letter: C, G, K, O climb by 4, so the next is S, not R. Its P and G also miss N and F.
• (c)
  PSOF — PSOF gets P, S and F right but not the third letter. F + 8 lands on N(14); O is 15, one step too far.
• (d)
  PSMF — PSMF also matches three letters. Its third letter M(13) is one short, because F + 8 is N(14), not 13.

A four-letter cluster series is four number series side by side. Read each column separately: here the first letter never moves, and the other three move by 4, 8 and 12.

The third and fourth columns run past Z along the way: X + 8 = 32, V + 12 = 34 and T + 12 = 32. Subtract 26 whenever a sum passes 26, so 32 becomes F and 34 becomes H.

Key facts

• Subtract 26 when a position passes Z: T + 12 = 32, and 32 − 26 = 6 = F.
• Each column of a cluster series can have its own step, found from the given terms.
• E5 J10 O15 T20 Y25 are handy anchors for letter-position arithmetic.

Common traps

• Stopping at 32 and looking for a 32nd letter instead of subtracting 26
• Miscounting F + 8 by one and choosing PSOF or PSMF

No directly related past PYQ was found.