Number bonds
Recall number bonds (addition and related subtraction facts) within 20
What a learner can do afterwards
- Quickly recall that 8 + 5 = 13
- Given 13 – 5, respond 8 using knowledge of related addition fact
- Know all pairs of single-digit numbers that sum to numbers up to 20
1 · Read
You already know many number bonds. Every bond makes two facts. One is adding. One is subtracting. If 8 + 5 = 13, then 13 − 5 = 8.
Ravi knows 8 + 5 = 13. His teacher asks 13 − 5. Ravi does not count. He just remembers the bond and says 8.
Stuck on a subtraction fact? Turn it into addition. Ask what number, plus the one you took away, makes the whole.
Know the addition fact, and its subtraction fact comes free.
More to read
Number Bonds
Number bonds are pairs that join to make a whole. Seven and three bond to ten, eight and five bond to thirteen. Learn the bonds and you never count from scratch. Split thirteen into eight and five any time you need it.
Number Bond Grids
Bond grids show every split of a number at once. Ten splits into nine and one, eight and two, seven and three, and more. Stare at the grid and say each pair aloud. Soon the pairs stick in your mind.
1.6: Properties of Addition
Addition facts come in families that share numbers. Eight plus five is thirteen, five plus eight is thirteen too. Thirteen take away five is eight, thirteen take away eight is five. Learn one bond and three more facts arrive free.
1.2 Add Whole Numbers
Big bonds build from small bonds you already know. Ten plus three is thirteen, so eight plus five is thirteen as well. Break five into two and three, add two to eight for ten, then add three. Making ten first turns hard sums easy.
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2 · Watch
به انگلیسیTake it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
18 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.