Addition and subtraction puzzles

Putting numbers together and taking them apart — and, on most of these boards, checking a total you kept in your head against a picture that disagrees with you.

Slug Salad is addition with a reason to go back: a slug is full when what it has just eaten equals everything before it, so a path either adds up or it does not. Hitome’s Paddocks counts the squares in a field and balances two flocks against each other until neither is ahead. Mondrian Puzzle and Galaxea both finish in a total you have to work out before you know how you did. Stained Glass belongs here because a skip count is repeated addition long before it is a times table.

6 puzzles

• Stained GlassSkip-counting turned into a picture: the pattern each times table draws across a hundred square. · grades 1–6
• Finding ZeroEvery number turned over says how far zero is, so the hunt closes in by reasoning rather than guessing. · grades 1–6
• Slug SaladEach slug eats a number equal to everything it has eaten before it — addition with a reason to check and go back. · grades 2–4
• GalaxeaTwo of the three dice are the sides of a rectangle — and the game is which two, and where to hang it. · grades 3–6
• Hitome's PaddocksA sheep is worth the squares in its own field, and the two flocks have to end up worth the same. · grades 2–6
• Mondrian PuzzleEvery rectangle painted is a multiplication, and the score is the gap between the biggest one and the smallest. · grades 2–6