Select the combination of letters that when sequentially placed in the blanks of the given series will logically complete the series. QUA_TO_ANT_UAN_KU_NT

Correct — B.

Rule: UANT repeats in every group, behind a head letter that steps back two places.

Cut the twenty letters into fives and the shape appears: QUA_T, O_ANT, _UAN_, KU_NT.

Filling the five blanks in order with N, U, M, T, A gives QUANT OUANT MUANT KUANT.

The heads are Q, O, M, K — positions 17, 15, 13 and 11, falling by two — and UANT never changes. That is option (b).

Why the others are wrong

• (a)
  NUTMA — NUTMA puts T at the third blank and M at the fourth, so the third group reads TUANM. The block is broken and the heads stop falling by two.
• (c)
  NULTA — NULTA makes the third group LUANT, so the heads run Q, O, L, K — falling by two, then three, then one. The tail is right but the head series is not.
• (d)
  NUTAM — NUTAM breaks two groups at once: the third reads TUANA and the fourth KUMNT. Neither is the repeating block.

Blank-filling letter series are solved by finding the period first, not by trying the four options one at a time.

Count the string: twenty characters, five of them blank. Twenty divides into four groups of five, and written that way the string reads QUA_T, O_ANT, _UAN_, KU_NT.

The letters U, A, N and T sit in the same places in every group. Only the head letter changes, and it changes regularly.

The question therefore reduces to reading four alphabet positions, with the blanks filled left to right across the whole string rather than group by group.

Key facts

• The string is twenty letters long and divides into four groups of five.
• Every group is one head letter followed by U, A, N, T.
• The heads are Q, O, M, K, at alphabet positions 17, 15, 13 and 11.
• Read left to right across the whole string, the five blanks take N, U, M, T, A.

Common traps

• Testing the options one by one instead of establishing the group length first
• Splitting the string into fours because UANT has four letters
• Filling the blanks group by group when they must be read across the whole string

No directly related past PYQ was found.