When multiplying four-digit numbers, we need to remember a few simple things. First, we solve each problem step-by-step. We first need to solve the problem in the ones place (ones column), then the problem in the tens place (tens column), and so on. Second, we regroup (carry) a digit. When we regroup, we must always remember this rule: first multiply, and then add. Following these two simple rules will help us solve our multiplication problems, no matter how great (large) the numbers are.
Here's a problem:
Let's start with the problem in the ones place. This is 7 times 4. How many is that? The answer equals 28. We write down 8 below the equal bar and regroup the 2.
The problem in the tens place is 7 times 4. How many is that? The answer equals 28, but remember, we regrouped 2 from the ones place. 28 plus 2 equals 30 (28 + 2 = 30). We write down 0 below the equal bar and carry the 3.
Now, the problem for the hundreds place (hundreds column) is 0 times 4. How many is that? Remember to treat 0 like any other number. 0 times 4 equals 0 (0 × 4 = 0). We add the 3 we regrouped from the tens place. This gives us 3. Since 3 is not a two-digit number, we do not have to regroup.
Finally, the problem for the thousands place (thousands column) is 7 times 4. We get 28. Since nothing was regrouped, we have nothing to add. Write down 28.
The product, or answer, to the problem is 28,308.
