We're going to put variables (letters) and numbers into number families. Remember that when a variable is used in a math problem, it represents an unknown number.
Here's the sentence: J equals 7 less than M. The first thing to do is to say the sentence without the number: J equals less than M.
That tells us how to put J and M in a number family. J equals less than M, so J must equal a lesser (smaller) number, and M must equal the greatest (largest) number. Now let's look at the sentence again with the number included. The whole sentence says that J equals 7 less than M. Where do we place the 7 in the number family? Well, we already know that J equals a lesser number and M equals the greatest number. That means that 7 must equal the other lesser number. It's the only place it can go.
We have our number family: J and 7 equal the lesser numbers, and M equals the greatest number. Even though we don't know what numbers J and M equal, we are able to place them in a number family.
Here's another problem to look at: R equals 15 more than K. First, say the sentence without the 15: R equals more than K. This means that R equals the greatest number, and K equals a lesser number. Now we know that the 15 equals the other lesser number. In this number family, K and 15 equal the lesser numbers, and R equals the greatest number.
