Select the option that represents the letters that when placed from left to right in the blanks below will complete the given letter series. M N _ O J K M _ Q O J K _ N Q _ J K M N Q O _ K M N

Correct — C.

Rule: the whole line is one six-letter block, M N Q O J K, repeated.

Write the 26 places out in groups of six and each blank names itself.

Group 1: M N _ O J K → the blank is Q
Group 2: M _ Q O J K → the blank is N

Group 3: _ N Q _ J K → the blanks are M and O
Group 4: M N Q O _ K → the blank is J
Group 5: M N — the block has started again and the line stops there.

Reading the blanks left to right gives Q, N, M, O, J = QNMOJ → option (c).

Why the others are wrong

• (a)
  QMNJO — Two pairs are swapped. QMNJO reverses the second and third blanks and then the fourth and fifth; the block opens M N Q, not M M N, and closes O J K, not J O K.
• (b)
  QNJMO — The third and fourth blanks are wrong. QNJMO puts J where a group's opening M belongs and M where O belongs — the third blank begins a fresh group, so it has to be M.
• (d)
  QNMJO — The last two blanks are the wrong way round. QNMJO is right up to the third blank, but the fourth sits in the O slot of _ N Q _ J K, not the J slot; J belongs to the group after it.

A gap-filled letter series is a periodic sequence with holes punched in it. Find the period first and the holes stop mattering.

Read along the line for the first stretch with no gaps. Here M N Q O J K appears intact, and the letters that follow repeat it, which confirms a block of six.

After that each blank is answered from its position inside its own group, not from the letters on either side of it. Neighbours mislead when two blanks fall in the same group, as they do here in group 3.

Key facts

• The line has 26 places and the repeating block M N Q O J K is six letters long.
• 26 is 4 times 6 plus 2, so the last group is the partial M N.
• Two of the five blanks, the third and the fourth, fall inside the same group.
• Once the block is known, each blank is fixed by its position in the group rather than by its neighbours.

Common traps

• Guessing the block length from the first three letters instead of testing it along the whole line.
• Swapping the fourth and fifth blanks, which sit in different groups.
• Miscounting the places and shifting every blank by one.

No directly related past PYQ was found.