Acorn Mystery Picture: Adding & subtracting to 100

An acorn with a textured brown cap, a short stem and a smooth orange nut ending in a little point. The cap shows up first, so children can guess the picture before they finish.

Problems use two-digit numbers up to 100, mixing those with and without regrouping: 36 + 27, 45 + 30, 82 − 49, 70 − 26. Children practice adding tens and ones separately, trading ten ones for a ten, and subtracting when the ones digit on top is too small, as in 82 − 49. Mental strategies such as adding 30 and then 6 work well here, and so do column methods on scrap paper.