Add, Subtract, Multiply & Divide Decimals

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  • 0:03 Decimals in Money
  • 0:28 Adding with Decimals
  • 1:22 Subtracting with Decimals
  • 1:59 Multiplying with Decimals
  • 2:51 Dividing with Decimals
  • 3:03 Lesson Summary
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Lesson Transcript
Instructor: Christine Quist

Christine has taught 4th-5th grade, has worked as a Paraprofessional for Adult Learners, and has a master's degree in Curriculum and Instruction for Elementary Education.

In this lesson, you'll learn about that tiny dot we call a decimal point, which is used to show part of a whole number. While having fun with some real-life problems, you'll learn how to add, subtract, multiply, and divide with the decimal point.

Decimals in Money

The main place you will see a decimal point is when you are working with money. The decimal point is a divider between whole numbers and parts of a number. When you have two dollars and seventy-five cents ($2.75), you have two whole dollars and a part of the third dollar. The point between the dollars and the cents is the decimal point. Remember to line up your numbers by place value from left to right, as shown here:

Place Value Chart

Adding with Decimals

Now, let's talk about adding decimals. Imagine you're at the market buying some carrots for soup. In one pocket you have thirty-five cents, and in the other pocket you have seventy-five cents. You need one whole dollar ($1.00) to buy the carrots. Now, let's find out if you have enough money:

Adding Decimals

1. First, line up the decimal points for the money: (.35 and .75)

2. Next, add the fives in the hundredths place to make one tenth, then carry the 1 so it's above the three in the tenths place

3. Add the 3 and the 7 in the tenths place to get 10 plus the 1 you carried, which will give you 1 whole number and 1 tenths: .35 + .75 = 1.10

At the end of the problem, make sure the decimal point always lands between the ones and tenths place. You have enough money!

Subtracting with Decimals

Now, let's talk about subtracting with decimals. Imagine you're the store cashier. The carrots still cost $1.00, and the customer has given you too much money: $1.10. You'll have to make change:

Subtraction 75

1. To figure this out, first line up the decimal points, and then subtract as you would with whole numbers

2. After subtracting 0 from 0, place the result (which is 0) in the hundredths column

3. Subtract 0 from 1, and place the 1 in the tenths column

4. Now subtract the whole numbers to get 0

The change you owe the customer would be $.010 (ten cents).

Multiplying with Decimals

When multiplying with decimals, there is a special trick to placing the point! Let's say you have to travel 3.5 miles to and from school every day five times a week. How many miles would you travel in one week?

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