Multiplication: Single-digit by Double-digit Numbers

Lesson Plan - Get It!

Audio:

We want to collect enough blankets so each dog has its own cuddly bed, which means we need to know how many dogs are at the shelter.

Remember, this is the information we already know:

• 24 dog pens with 3 dogs in each pen

There are three ways to find the total number of dogs:

• You could count each dog, but that would take forever!
• You could use repeated addition and add 3, 24 times.
  • 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 + 3 = ?
• OR, you could multiply 3 by 24!

Multiplication is the best method to figure out how many blankets we need to collect!

First, look at the factors, or the numbers being multiplied together, in this equation.

• What do you notice about the numbers 3 and 24?

I bet you noticed that 3 is a one-digit number and 24 is a two-digit number. You know that 24 is made up of 2 tens and 4 ones.

Let's use an area model to help us multiply these two numbers.

When using an area model, the two factors of the equation are on the top and side of the model. The factor 3 is on the side, and the factor 24 is represented on the top of the model.

Since 24 can be broken into 20 and 4, we will write that on the top of the area model.

Now, we will multiply 3 x 20.

Next, we multiply 3 x 4.

The last step is to add the two products together to find the answer. So, 60 + 12.

We have a final answer!

There are 72 dogs at the animal shelter!

Wait! Let's double check our answer before we start collecting all those blankets. There is one more way to multiply 3 x 24.

Instead of drawing an area model, we will solve for the product by placing the factors on top of each other.

You need to make sure the 3 is perfectly under the 4 since both of those numbers represent the ones place. Since 3 is a single digit, nothing goes under the 2. 2 is the only number in the tens place.

Now, we can multiply. First multiply the ones place, so 3 x 4. The product is 12, but we can only write one number in the ones place. Write the 2 in the ones place under the line. Since the 1 is in the tens place, we will write it above the tens place. You will use that 1 later.

Next, multiply the 3 times the tens place. 3 x 2 = 6. But, don't forget that 1 we wrote earlier! Add the 1 to the product you just got. So, 6 + 1 = 7. You will write the 7 under the line in the tens place.

Look at the final product! We solved for 72 again!

So, I guess we need to collect 72 blankets for the 72 dogs in the shelter!

Next, visit the Got It? section to help figure out how many supplies we need for the cats at the shelter.