Math Topics 4

4-1 - Multiplying Decimals by Powers of Ten and 4-2 - Estimating Products with Decimals

100

4.8 x 10⁴ = ?

? = 48000

200

4.8 x 0.01 = ?

? = 0.048

300

Is 6.439 x 10¹ 10 or 100 times larger than 6.439 x 0.1?

100 times larger

64.39 / 100 = 0.6439 or 0.6439 x 100 = 64.39

400

Write and solve an equation to estimate the product of 120 x 0.75 using rounding to the nearest whole number.

120 x 1 = 120

500

Write and solve an equation to estimate the product of 120 x 0.75 using compatible numbers.

100 x 0.8 = 80

4-3 - Using Models to Multiply Decimals by Whole Numbers and 4-4 - Multiplying Decimals by Whole Numbers

100

2.5 x 9 = ?

22.5

200

A Lambo drives 162.35 miles in 1 hour.

A Ferrari drives 184.55 miles in 1 hour.

If both cars drive for 2 hours, how much farther does the Ferrari drive than the Lambo?

184.55 - 162.35 = 22.20 

22.20 x 2 = 44.40 more miles

300

How would you fill out a 10x10 grid to represent 0.6 x 0.3?  What is 0.6 x 0.3?

Fill out 6 of the 10, or 0.6, columns of 3 of 10, or 0.3, rows.

400

4 x .22 = ?

40 x .22 = ?

400 x .22 = ?

.88

8.8

88

500

Kai plays Prodigy for 1.65 hours every day.  If he plays for the same amount of time every day for a week, how many hours does he play in all?

11.55 hours

4-4 - Multiplying Decimals by Decimals and 4-6 Multiplying Decimals Using Partial Products

100

0.3 x 0.5 = ?

0.15

200

What is the difference between 4 x 8 and 0.4 x 0.8?

4 x 8 = 32

0.4 x 0.8 = 0.32

32 is 100 times bigger than 0.32

300

Use partial products to solve 2.4 x 1.5.

2 x 1 = 2

2 x 0.5 = 1

0.4 x 1 = 0.4

0.4 x 0.5 = 0.20

2 + 1 + 0.4 + 0.2 = 3.6

400

1.5 x 4.2 = ?

6.30

500

Kai buys shortbread cookies that cost $4.50 per pound.  If he wants to buy 2.1 pounds of cookies, how much will that cost?

$4 x 2 = $8

$4 x 0.1 = $0.40

$0.50 x 2 = $1

$0.50 x 0.1 = $0.05

$8 + $1 + $0.40 + $0.05 = $9.45

4-7 - Using Properties to Multiply Decimals

100

What is the product of 1.4 x 0.81?

1.134

200

Anna runs 1.2 miles.  Her mom runs 8.75 times farther than her.  How far does Anna's mom run?

10.500 miles

300

What expression is equivalent to 3.6 x 0.64?

A (36 x 64) x (1/10 x 1/10)

B (36 x 64) x (1/10 x 1/100)

C (3.6 x 0.64) x (1/10 x 1/10)

D (3.6 x 0.64) x (1/10 x 1/100)

B (36 x 64) x (1/10 x 1/100)

400

What expression is equivalent to 0.3 x 0.4?

A (3 x 4) x (1/10 x 1/10)

B (0.3 x 0.4) x (1/10 x 1/10)

C (0.3 x 0.4) x (1/100 x 1/100)

D (3 x 4 ) (1/100 x 1/100)

A

500

Use the associative property to rewrite x 3.4 x 2 x 2.5 to make it easier to solve.

(3.4 x 2) x 2.5 = 3.4 x (_____ x ______)

Then, solve.

= 3.4 x (2 x 2.5)

= 3.4 x 5 = 17

4-8 - Using Number Sense to Multiply Decimals and 4-9 - Multiplying Decimals

100

True or False: There are 3 decimals in the product of 4.12 x 3.5 

True.

200

Is the decimal in the correct position of this product? If not, where does it go?

4.4 x 2.73 = 120.12

No, the decimal should be between the 2 and 0.

4.4 x 2.73 = 12.012

300

Which two factors would give me a product of 5.1?

A) 3 and 0.17

B) 0.3 and 1.7

C) 0.3 and 17

D) 0.3 and 0.17

E) 3 and 1.7

C and E

400

Find the product of 1.5 x 1.1 using the standard algorithm.  Use 15 x 11 and counting decimal places to help you solve.

1.5 x 1.1 = ?

1.65

500

Juni read books on Epic for 0.67 hours on Tuesday.  Kai read 4.4 times the amount that Juni read.  How long did Kai read for? Use the standard algorithm to solve.

2.948 hours