Multiplying decimal numbers

Multiplying

decimal numbers

​

Add, subtract, multiply, and divide decimals to hundredths using strategies based on place value, properties of operations, and/or the relationships between addition/subtraction and

​multiplication/division; relate the strategy to a written method, and explain the reasoning used. Use concrete models and drawings to solve problems with decimals to hundredths. [5.NBT.8a]

When multiplying decimal numbers . . .

Remember the steps!

1. Estimate your answer (check the reasonableness)

2. Line up the numbers from the right (leave or remove the decimals – your choice!)

3. Solve using long multiplication

4. Count the numbers after the decimal points*

5. Place the decimal point in front of the digits you counted in step 4

6. Compare your answer to your estimate from step 1

*Shortcut! The number of digits after the decimal place is how many spaces from right to left you will move when placing your

​decimal into your final answer.

Examples:

47.51 x 8

​

47.51

x 8

______

​380.08

Decimals | Math 5

*Use long multiplication to help you solve.

​5.7 x 10

​

5.7

x 10

_____

​57

​*Multiplying by 10 is easy peasy - just move the decimal over to the right one place!​

Multiple Choice

How many places and which direction should we move the decimal when we multiply any number by 10?

(Remember, 10 is a whole number!)

Example: 4.2 x 10

• one space to the left

• one space to the right

• two spaces to the left

• two spaces to the right

Multiple Choice

Derek has a collection of ten model cars. Each car is 3.25 inches long. If he lined up his cars in a row, how many inches long would the entire collection be?

• 325 inches

• 32.5 inches

• 0.325 inches

• 0.0325 inches

Fill in the Blanks

Multiple Choice

How many numbers will be behind the decimal in our answer for 0.2 x 0.8?

• 1

• 2

• 3

• 4

Each small individual square​ represents a hundredth (.01). Each column (up and down) and each row (left to right) represents a tenth (.10).

​

Shading in a grid is very helpful when multiplying fractions!

​When modeling . . .

​

Multiple Choice

Solve the following problem:

0.4 x 7

Use the grid if it helps!

• 2.8

• 28

• 0.28

• 280

Multiple Choice

Solve the following problem:

0.2 x 3.4

Use the grid if it helps!

• 3.6

• 2.34

• 0.68

• 0.36

Poll

How do you feel about multiplying decimals?

• 1: I am going to need lots of help with this.

• 2: I think I get it, but I may still need some help.

• 3: I get it; I just need more practice.

• 4-5: I can almost teach it, and/or I can definitely show that I know it.

Open Ended

Hitting a snag?

How can I help you better understand multiplying decimals?