Select the option that represents the letters that when placed from left to right in the blanks below will complete the given letter series. P Q _ S _ P P Q P _ A P P Q _ S A P _ Q

Correct — B. The series is one block of six letters, repeated.

Rule: the block is P Q P S A P.

Write the twenty terms in rows of six and the columns line up:

P Q _ S _ P
P Q P _ A P
P Q _ S A P
_ Q

Row 2 shows position 3 as P, row 1 shows position 4 as S, row 2 shows position 5 as A. The block is fixed.

Reading the five blanks in order gives P, A, S, P, P — option (b).

Why the others are wrong

• (a)
  PQSAP — The second blank is filled with Q, but that blank is position 5 of the block, and rows 2 and 3 both print A there.
• (c)
  QPASP — This puts Q in the first blank, which is position 3 of the block. Row 2 prints that position as P, so it cannot be Q.
• (d)
  QSPAP — Two errors at once: Q at position 3 and S at position 5. Both positions are already visible in later copies of the block.

A letter series with scattered blanks is almost always a fixed block repeating. Find the block length first, then read each blank off a copy of the block that already shows that position.

Look for a repeat you can see rather than guessing. Here P Q appears at terms 1, 7 and 13 — six apart — so the block is six letters long.

Written in rows of six, the series becomes a grid, and every blank has a filled neighbour in its own column.

Key facts

• The repeating block is P Q P S A P.
• P Q occurs at terms 1, 7 and 13, six terms apart.
• The twenty terms are three complete blocks followed by P Q.

Common traps

• Guessing the block length from the opening letters instead of from a visible repeat.
• Filling the blanks left to right by feel rather than by column.
• Miscounting the terms, which shifts every column by one and breaks the grid.

No directly related past PYQ was found.