Fact Families: Three Numbers That Build Four Number Sentences

You will meet this idea in ordinary days. Families of numbers work like families of people. The members stay the same even when they stand in a different order. This is worth learning because fact families cut your memory work down to a quarter of the size. Watch for it today, and when you spot it, tell someone what you noticed and how you knew.

Here is today’s math treasure. Three numbers that belong together make a fact family. Take 4, 6, and 10. You can write four sentences: 4 plus 6 equals 10, 6 plus 4 equals 10, 10 minus 4 equals 6, and 10 minus 6 equals 4.

The whole is ten and the parts are four and six. Learn one family and you have learned four facts at once, which is a very good bargain.

Try building one from scratch. Pick three numbers where two of them add to the third, like 5, 7, and 12. Write your four sentences. If a sentence comes out false, one of your three numbers does not belong to that family. Take your time. Careful is better than fast.