Turtle Mystery Picture: Adding & subtracting to 30

A turtle seen from the side, with a patterned green shell, a little head and stubby legs. The rounded shell appears first, and the head with its eye gives the picture away at the end.

Children add and subtract with numbers up to 30 and cross ten along the way: 17 + 6, 26 − 8, 19 + 5, 30 − 12. Since every answer has to match a row on the grid, results never go past the height of the picture, and the bigger numbers appear mostly as the starting number in a subtraction, such as 27 − 9 or 24 − 7. That makes this topic particularly strong on subtracting across a ten from the twenties, which many children find harder than adding.