Easy Decimal Arithmetic: All Operations!

Lesson Plan - Get It!

Audio:

You aren't at a football game getting ready to watch your team score, but you are ready to score some points by adding, subtracting, multiplying, and dividing decimals correctly.

Get started by reviewing the arithmetic rules for decimals!

Adding and Subtracting Decimals

1. Key first step: Make sure your decimals are lined up. Rewrite all problems vertically, up and down!

2. Add or subtract as normal.

3. KEEP the decimal right where it was and drop it down into your answer.

4. You are done!

NOTE: If you have a problem with a number showing in a certain spot, you can put a 0 there for it. But remember, make sure your decimals are lined up!

Examples

8.2 + 2.11

Rewrite, and line up the decimals.

2.2 - .14

Rewrite, and line up the decimals.

Multiplying Decimals

1. Rewrite and multiply as normal. Ignore the decimal points.

2. Count how many numbers were behind each decimal in the problem to start.

3. Use that total to count over from the right that many places in the answer, and you've got it!

NOTE: When you rewrite the problem vertically (on top of each other), you can always put the "longer" number on top. The decimals DO NOT have to line up!

Example

1.2 x 3.25

Dividing Decimals

If the decimal is in the first number (dividend), follow these steps.

1. Divide normally, as if the decimal isn't there.

2. At the end, bring the decimal straight up from where it is so it is in that same place in the answer.

If the decimal is in the second number (divisor), follow these steps.

1. Shift the decimal in the dividend until you have a whole number.

2. However many places you moved it in the divisor, you also have to move it that many places in the same direction in the dividend.

3. Then, divide as normal, bringing the decimal straight up into the answer!

Jump over to the Got It? section to watch a division example. Pay close attention, and don't be afraid to watch it more than once.