A number family is made up of numbers that always go together in addition and subtraction. Look at these two examples:
These groups of numbers are what you call number families. The numbers 3, 4, and 7 make up the first number family. Do you know what number families can tell you? A number family gives you facts about the numbers. One addition fact for the first family is 3 plus 4 equals 7 (3 + 4 = 7). The other is 4 plus 3 equals 7 (4 + 3 = 7). One subtraction fact is 7 minus 4 equals 3 (7 - 4 = 3). The other is 7 minus 3 equals 4 (7 - 3 = 4).
Let's do the same for the second family. The addition facts are 4 plus 5 equals 9 (4 + 5 = 9) and 5 plus 4 equals 9 (5 + 4 = 9). The subtraction facts are 9 minus 5 equals 4 (9 - 5 = 4) and 9 minus 4 equals 5 (9 - 4 = 5).
These facts are easy to remember. Look at the number families again. The greatest (larger) number is always at the end of the arrow. In the first family, the greatest number is 7. The lesser (smaller) numbers are above the arrow. In the first family, the lesser numbers are 3 and 4.
What is the greatest number in the second family? Look for the answer at the end of the arrow. The number 9 is at the end of the arrow. It is the greatest number.
What would you do if you saw a number family with the greatest number missing? How would you find that number? Don't worry, it's easy to do. If the greatest number is missing, you add the lesser numbers.
For example:
If you add the lesser numbers 2 and 4, the sum will be 6. So 6 is the greatest number. Isn't it simple?ญ
