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
Explanation: The diagram contains 3 sets of 4 letters - one set of outer corner letters, one set of inner corner letters, and one set of letters on each side of the square. The numerical values of the letters in each set add up to 40.
Explanation: In each row, add together the numerical values of the pairs of letters to the left and right, then calculate their difference, putting the letter with this numerical value in the centre space.