Multiplication and Division
Multiplying 2- and 3-Digit Numbers
Solving Stacked Multiplication Problems
At first glance, stacked multiplication problems might look pretty complicated. Don't worry! If you can solve the problems in Lesson 1, you can learn to solve these problems too. To multiply large numbers, you'll use the same basic skills you use to multiply small ones. You can even use the same tools, like times tables.
Let's see how solving stacked multiplication problems works.
Remember the example of two boxes that each had 14 pears each? To find out how many pears there are total, we'll solve this problem: 14 x 2.
When you multiply stacked numbers, you start with the right digit in the bottom number of the problem. Our bottom number only has one digit: 2.
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We'll multiply 2 by the top number, 14. Since there's no 14 in the times table, we'll have to multiply one digit at a time.
As usual, we'll solve the problem from right to left. So, we'll multiply 2 by the digit on the top right. Here, that's 4.
Now it's time to solve 2 x 4. We can use the times table.
2 x 4 is 8. We'll write 8 below the 2 and 4.
Now we'll multiply 2 by the next digit to the left: 1.
Now we solve 2 x 1.
Whenever you multiply a number by 1, that number stays the same. So 2 x 1 is 2. Just to be sure, we'll check the times table.
Write the 2 beneath the line, directly below the 1.
We're done! Our total is 28, or twenty-eight. 14 x 2 = 28.
Let's practice with another problem, 31 x 7.
Always start with the digit on the bottom right. Here, that's 7.
First, multiply 7 by the digit on the top right, 1.
7 x 1 is 7. Write the 7 directly below the digits we just multiplied.
Next, we'll multiply 7 by the next digit to the left. That's 3.
We'll use the times table to solve for 7 x 3.
7 x 3 is 21. Make sure to line the numbers up so that the right digit of 21, 1, is directly under the 3.
Our answer is 217. So, 31 x 7 = 217.
Now you try it. Solve these multiplication problems. Remember, you can always use a times table for help. For now, ignore the box that appears above the numbers on the right.
