### Multiplying with decimals

In Adding and Subtracting Decimals, you learned how to **add** decimal numbers. You may be able to think of times when you'd add decimals in real life. For example, let's say you go to the store and find a shirt you really like. The price tag says it costs $15.60. You like the shirt so much that you decide to buy five of them.

To figure out the total cost, you could **add** the prices.

Adding this many numbers could take a long time. In the lesson on multiplication, we learned that when you multiply, you are **increasing** a number many times. Because all of the shirt prices are the **same**, multiplication could help you solve this problem a little faster.

When you multiply decimal numbers, it's helpful to set up the problem in a way that makes it easier for you to solve it** one step at a time**.

Click through the slideshow below to learn how to set up a multiplication problem with decimals.

Instead of adding $15.60 + $15.60 + $15.60 + $15.60 + $15.60...

Instead of adding $15.60 + $15.60 + $15.60 + $15.60 + $15.60...we'll multiply $15.60 by 5.

Let's set up our multiplication expression: $15.60 x 5. We'll stack the numbers one on top of the other.

It's a good habit to place the number that has the **most** digits on **top**. This makes the problem easier to solve.

Let's look at the number of **digits** in each number. 15.60 has **four** digits...

Let's look at the number of **digits** in each number. 15.60 has **four** digits...and 5 is **one** digit.

15.60 has more **digits**. This means we'll write 15.60 **above** the 5.

Since we're multiplying this number, we'll write the **times sign** (X) to the **left** of the numbers.

Instead of an **equals sign **(=), we'll put a **line** underneath the number on bottom.

When writing a stacked multiplication expression with decimal numbers, the numbers should be lined up on the **right**.

Let's look at another example. We'll stack this expression: 4.5 x 38.12.

First, let's look to see how many **digits** are in each number. 4.5 has **two** digits...

First, look to see how many **digits** are in each number. 4.5 has **two** digits...and 38.12 has **four** digits.

38.12 has **more** digits. This means we'll place 38.12 above 4.5.

Then we'll make sure the digits to the **right** are lined up. The 2 is right **above** the 5.