March 21st Decimal Operations

Adding Decimals

To add decimals start by writing the amounts out and lining them up by the decimal points.

Multiple Choice

What is the first step in adding or subtracting decimals?

• Adding or subtracting

• Putting 0's in for missing place values

• Lining up the decimas

• Dropping decimal in answer

Multiple Choice

Try this:

$$42.46\ +\ 10.44$$  

• 529

• 52.9

• 52.80

Multiple Choice

0.304 + 0.05

• 0.354

• 0.854

• 0.804

• 0.309

Subtracting Decimals

Subtracting decimals is similar to adding decimals. When subtracting decimals you are going to write out the two pieces to the problem by lining up the decimal points.

Things to remember

• We line up the numbers by their decimal points to make sure they are in the correct place value when adding/subtracting

• When adding be sure you are regrouping when needed

• When subtracting be sure you are borrowing when needed

Multiple Choice

Try this:

$$5.18\ -\ 2.30$$  

• 2.28

• 2.88

Multiple Choice

5.4-2.43

• 3.01

• 2.97

• 3.97

• 1.34

Multiple Choice

Find the difference $18- $3.55

• $14.55

• $14.41

• $14.45

• $14.56

Multiplying Decimals

• When you multiply decimals you do not line up the problem by the decimal points

• Starting from the right side of each number, count how many decimal places you have with each number

• Multiply as you usually would, starting from the right and working to the left

• Write down the amount of decimal places there are to the right of. the problem and circle it

Multiple Choice

Try this:

$$5.05\ \times\ 3.1$$  

• 1.5655

• 156.55

• 15.655

Multiple Choice

11.3 x 2.5

• 79.1

• 13.8

• 22.597

• 28.25

Multiple Choice

Oliver bought 7 bags of candy. Each bag costs $1.50. How much money did he have to pay?

• $7.50

• $8.50

• $10.50

• $105.00

Multiple Choice

Tyler bought 3 fishing lures for $3.99 each. How much was the total for all lures?

• $11. 97

• $ 12.00

• $ 10.95

​Dividing Decimals with Decimals in the Dividend

• ​Identify the dividend and divisor in your problem.

• ​Rewrite the division problem using the division house with the dividend under the "house".

• ​Place a decimal point in the quotient by lining it up with the quotient.

• ​Divide normally (think: how many times the divisor can "fit into" the dividend.

​

​Dividing Decimals with Decimals in the Dividend and Divisor

• Rewrite the problem in the division house.

• ​STEP 1: Move the decimal point in the divisor to the far right of the divisor to make it a whole number.

• STEP 2: ​Move the decimal point the SAME NUMBER of places in the dividend.

• ​STEP 3: Write a decimal point in the quotient above the decimal point in the dividend.

• ​Divide as usual.

Multiple Choice

Try this:

$$8.5\ \div5$$  

• 1.7

• 17

Multiple Choice

Try It! Find the Quotient:

$$48.4\ \div\ 0.4$$  

• 1.21

• 0.21

• 121

• 12.10

Multiple Choice

7.8 ÷ 0.03 =

• 2.6

• 26

• 260

• .26

Multiple Choice

Calculate

0.6÷5

• 0.1

• 0.12

• 0.012

• 1.02

Multiple Choice

Lee ordered 5 t-shirts for his friends and paid $54.95 for all of them. How much did each shirt cost?

• $49.95

• $8.90

• $10.99