Missing Ten Puzzles: Figuring Out What Was Taken Away

This is not just for paper. Real problems often hide the middle piece. A shopkeeper knows the start and the end and works out what happened between. This is worth learning because missing piece problems train the flexible thinking algebra will need.

Watch for it today, and when you spot it, tell someone what you noticed and how you knew. Ask yourself where else the same idea might be hiding, then go and look.

You are going to like this one. Try a puzzle. Sixty take away something equals forty. What left? Count up by tens from forty to sixty: fifty, sixty.

Two jumps, so twenty was taken away. Try another: something take away thirty equals fifty. Add thirty back to fifty and you find eighty. These puzzles use everything you know about tens, and they feel like riddles rather than practice, which is a pleasant trick.

Try making up one of these for someone else. Give them a start and an end and let them find the middle. Writing a good puzzle is harder than solving one, and it shows you understand the structure. Little by little, this becomes something you just know.