Puzzles - Missing letters puzzles

Start at the top left, and work through the diagram in a Z shape, letters move through the alphabet in steps of 6, then 7, then 8 etc.

Start on the top left and move down, then right one space and up etc in a snakes and ladders pattern. Letters advance through the alphabet in steps of 5.

Start with the letters in the left hand circle. Subtract 3 from the numerical values of each letter, and put the letter with this value in the corresponding segments of the upper circle. Repeat this pattern, adding 3 to the numerical values of the letters, and putting the results in corresponding segments of the lower circle.