Puzzle 1: Which letter replaces the question mark?
Answer: R
Explanation: Working from top to bottom, letters move through the alphabet in steps of 2, then 3, then 2 etc.
Puzzle 2: Which letter replaces the question mark?
Answer: I
Explanation: Starting with the top two segments, the sum of the numerical values of letters in adjoining segments equals 20.
Puzzle 3: Which letter replaces the question mark?
Answer: C
Explanation: The sum of the numerical values of the letters in each column of the diagram equals 29.
Puzzle 4: Which letter replaces the question mark?
Answer: U
Explanation: The sum of the numerical values of the letters in opposite segments of the circle equals 26.
Puzzle 5: Which letter replaces the question mark?
Answer: J
Explanation: Start with the letter J in the top Left Square, and move clockwise around the other squares. Letters follow the alphabetic sequence, skipping 4 letters at a time. Start with the X in the inner square in the top left, and move clockwise. These inner letters also follow the alphabetic sequence, skipping 5 letters at a time.