Addition and subtraction within 20

Addition to 20 and subtraction within 20

Addition to 20 and subtraction within 20 are the core of 1st grade: 9 + 6, 15 − 7, 12 + 5. By the end of 2nd grade the Common Core expects children to know all sums of two one-digit numbers from memory, and in England pupils should recall addition and subtraction facts to 20 fluently in Year 2. The games on this page mix easy facts (12 + 5) with the ones that cross ten (8 + 5), because those are the facts that take practice.

The make-10 strategy for adding to 20

The hardest addition facts within 20 are the ones that go over 10: 7 + 5, 8 + 6, 9 + 4. Children who know their number bonds to 10 can split the second number: 9 + 4 → 9 + 1 + 3 → 10 + 3 = 13. The number line picture shows the two jumps. It sounds long, but after some practice the steps happen in a second, and the same thinking later works for 38 + 5 and 280 + 40.

Subtraction within 20 the same way

For 13 − 5, take away 3 to get to 10, then 2 more: 8. Or think addition: "5 and what makes 13?" Both are fine; the game shows both ways in its hints.

Games for within 20

The trainer is the base game: one question, four answer buttons, missed facts repeated. In the gates runner the task line asks for "exactly 17", so the child plans which gate to take. Make 20 asks for pairs like 13 and 7. The speed test is the best way to check fluency: when the answers come without counting, the score jumps. All four play online. For adding and subtracting within 20 on paper, print the addition and the subtraction sheets with answer keys, or the "crossing 10" sheet to practice the strategy on paper.

A tip for parents

Ask for the strategy, not only the answer: "How did you get 14?" A child who says "8 and 2 is 10, and 4 more" is ready for bigger numbers; a child who counted on fingers needs a few more rounds of Make 10.