What comes next? Z, X, U, Q, ?

Correct — A.
Rule: backward steps of 2, 3, 4, 5 (the gap grows by one).

Z(26) − 2 = X(24)
X(24) − 3 = U(21)
U(21) − 4 = Q(17)
Q(17) − 5 = L(12) → option (a).

Why the others are wrong

• (b)
  M — M(13) is Q − 4, repeating the last step. The gap grows every time, so after 4 comes 5, which lands on L.
• (c)
  N — N(14) is Q − 3, a smaller step than the one before. The gaps run 2, 3, 4, so the next must be 5, not 3.
• (d)
  P — P(16) is Q − 1, as if the letters stepped back one at a time. The gaps here grow, 2, 3, 4, so the next is 5.

A letter series becomes a number series once each letter is replaced by its place in the alphabet (A = 1 … Z = 26). Write the numbers, then write the differences under them.

Here the letters run backwards from Z and the differences grow by one: 2, 3, 4. The next difference is 5, so 17 − 5 = 12, which is L.

Key facts

• Z = 26, X = 24, U = 21, Q = 17 and L = 12.
• The gaps 2, 3, 4, 5 grow by one at each step.
• The anchors E = 5, J = 10, O = 15, T = 20 and Y = 25 speed up turning letters into positions.

Common traps

• Repeating the last step of 4 and choosing M
• Miscounting positions near the end of the alphabet by one

No directly related past PYQ was found.