Number bonds to 10

A number bond shows a whole and its two parts. When one part is unknown, the missing addend is the whole minus the known part.

A number bond says the parts add to the whole, and writing 3 + 4 = 7 uses the equal sign to say both sides are the same amount.

Each number bond gives a fact family: if 3 and 4 make 7, then 3 + 4, 4 + 3, 7 - 3 and 7 - 4 all describe the same bond.

Breaking a factor into parts, like 23 into 20 and 3, gives the partial products an area model adds up.

The bonds of 5 are the pairs 0 and 5, 1 and 4, and 2 and 3, which are exactly the facts within 5.

A group split into two sorted parts is a number bond: 8 shapes are 5 red and 3 blue.

Splitting a number into two parts is the same move as splitting an array into two smaller arrays whose totals add.