Fact Families Within 20

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Grade 1MathAddition & SubtractionCCSS 1.OA.B.4CCSS 1.OA.C.6

Skill: Writing the addition and subtraction facts in a fact family

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10 versions, each with its own answer key

Same skill and layout, a fresh set of problems in every version, so children can keep practicing without repeating a page. Problems are not repeated between versions unless a skill has only a small number of possible problems (for example, the addition facts within 10).

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About this worksheet

A fact family is a group of three numbers that work together in addition and subtraction. The numbers 4, 9, and 13 make four facts: 4 + 9 = 13, 9 + 4 = 13, 13 - 4 = 9, and 13 - 9 = 4. Seeing them as one family shows that subtraction undoes addition. This first-grade worksheet gives six fact families within 20. Each family is shown as a number triangle with the total at the top and the two parts at the bottom. Children write two addition facts and two subtraction facts for every triangle.

The two parts in each family are always different numbers, so every family has four different facts. Totals range up to 20, which matches the first-grade goal of adding and subtracting within 20.

How to use it: start with the triangle. Cover the top number and ask, "What do the two bottom numbers make together?" Then cover one bottom number and ask, "If we take this part away from the total, what is left?" Point out that the biggest number always comes first in a subtraction fact. The two addition facts can be written in either order, and so can the two subtraction facts.

The answer key lists all four facts for every family. This worksheet supports Common Core standards 1.OA.B.4 (understand subtraction as an unknown-addend problem) and 1.OA.C.6 (add and subtract within 20). Try it after our Addition Within 20 and Subtraction Within 20 worksheets.