Number Bonds Practice
Find the missing part that completes the bond.
About number bonds practice
A number bond shows a whole number split into two parts. The diagram shows the whole at the top and both parts below it — one part is already filled in, and the other is missing. Type the number that completes the bond so the two parts add up to the whole exactly.
This is a different skill from straightforward addition practice: instead of being given both numbers and asked for the total, you're given the total and one piece of it, and have to work out what's missing. That's the foundation for mental math strategies taught later, like using known bonds to 10 to add larger numbers quickly.
Bonds to 5 is the simplest starting point, Bonds to 10 is the most commonly practiced level, and Bonds to 20 extends the same idea further. The missing part appears on either side of the diagram at random, since a bond works the same way regardless of which side is shown.
Frequently asked questions
What exactly is a number bond?
A pair of numbers that add up to a target "whole" — for bonds to 10, that includes every pair from 0+10 up through 10+0.
How is this different from regular addition practice?
Regular addition gives you both numbers and asks for the total. Number bonds gives you the total and one part, and asks for the missing part — the reverse direction, which is what builds the mental-math skill of breaking numbers apart and back together.
Why does the missing part sometimes appear on the left and sometimes the right?
A bond doesn't depend on which part is listed first, so mixing up the position keeps the practice from becoming just "always fill in the right-hand circle."