Think of number families that have only one-digit numbers. Finding the missing lesser (smaller) number or the greatest (larger) number in those number families is simple. All you have to do is remember these two rules: If the greatest number is missing, you add. If a lesser number is missing, you subtract.
But what if a number family has two-digit numbers? Do you know how to find the missing lesser or greatest number? Here's how to do it:
When a number family has two-digit numbers, we can write a column subtraction problem. Let's begin by knowing if the lesser or greatest number is missing in a number family.
For example:
the greatest number missing in this family? A lesser number is missing. So we write a subtraction problem: 36 minus 22 equals how many? This might look harder for you to solve because these are two-digit numbers. Using column subtraction will make it easier.
When we write the problem in a column, we don't need a box.
Here's another number family:
Is a lesser number or the greatest number missing in this family? It's a lesser number. Since the number family has two-digit numbers, what do we do to find the missing lesser number? We write a column problem. Can you do that?
Now you can rewrite two-digit subtraction problems in column form.
