Complete the letter series: A, C, F, J, ?

  • A. M
  • B. N
  • C. O
  • D. P

Explanation

The gaps between the letters grow by one each step: A to C skips one letter, C to F skips two, F to J skips three, so the next step skips four and lands on O. Writing the alphabet with position numbers turns this into the numeric series 1, 3, 6, 10, 15, which is the triangular numbers. The answer M comes from assuming a constant gap of three.

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