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24. Which letter should replace the question mark?
  IQ test. Accurate and free online iq test # 4 with answers and solutions. Question # 24. Which letter should replace the question mark?
 

Explanation:
The alphabetic number of the next letter is multiplied by 2 (from left to right). In terms of the alphabetic order of letters. F × 2 = L; L × 2 = X.