Estimation
Multiply by 10's
What's your strategy?
Properties
Problem Solving
100
Estimate:

34 x 87

30 x 90 = 2,700

100

34 x 10 = 

30 x 10 = 300

4 x 10 = 40

300 + 40 = 340

100

What are the partial products?

46 x 35 = 

5 x 6 = 30

5 x 40 = 200
30 x 5 = 150
30 x 40 = 1,200

100

What is the expanded form?

57 x 65

(50 + 7) x (60 + 5)

100

Joey reads 15 pages of his book each night for two weeks.  How many pages does he read altogether?

15 x 14 = 210 pages

200

Estimate:

72 x 52

70 x 50 = 3,500

200

75 x 40

70 x 40 = 2,800

5 x 40 = 200

2,800 + 200 = 3,00

200

Solve:

43 x 89 = 

3,827

200

What is the missing piece of this property?

59 x 76 = 76 x ____

What property is this?

59

Commutative Property

200
A cleaning service charges $13 for floors and $25 for bathrooms.  If the service cleans 27 total floors and bathrooms, how much money did they make?

13 + 25 = 38

38 x 27 = $1,026

300

Estimate:

82 x 93

80 x 90 = 7,200

300

85 x 30 = 

80 x 30 = 2,400

5 x 30 = 150

2,400 + 150 = 2,550

300
Are these partial products correct?

56 x 89 =

9 x 6 = 56
9 x 50 = 450
80 x 6 = 4,800
80 x 50 = 400

NO!!
9 x 6 = 54
9 x 50 = 450
80 x 6 = 480
80 x 50 = 4,000

300

Identify this property:

6,977,887 x 1 = 6,977,887

Identity Property of Multiplication

300

Larry runs 18 laps 16 times in June 

and 19 laps 15 times in July.  How many total laps

did Larry run?

June: 18 x 16 = 288 laps

July: 19 x 15 = 285 laps

288 + 285 = 573 total laps 

400

Estimate:

13 x 76

10 x 80 = 800

400

23 x 90 = 

20 x 90 = 1,800

3 x 90 = 270

1,800 + 270 = 2,070

400

Is this product REASONABLE?

57 x 50 = 2,850
50 x 50 = 2,500

No,

57 rounds to 60
60 x 50 = 3,000 

400

Fill in the missing piece:

78 x (34 x 12 ) = (78 x ___) x 12

Associative Property of Multiplication

400

Melissa needs 38 beads for every necklace she is making.  If she needs to make 58 necklaces for the holidays, what is the BEST ESTIMATE for how many beads she may need?

38 x 58 =

40 x 60 = 2,400 total beads

500

Estimate: 

58 x 86

60 x 90 = 5,400

500

77 x 70 = 

70 x 70 = 4,900

7 x 70 = 490

4,900 + 490 = 5,390

500

What is the missing factor?

____ x 30 = 2,400

80 x 30 = 2,400

500

If you multiply this number times ANY number the answer is always zero...
WHAT IS IT?

Zero!!

500

Johnny delivers 23 pizzas on Friday and 17 pizzas on Saturday.  If he earns an average of $2 per pizza, how much money will he make in one month? (Remember, there are 4 weekends in one month?

23 + 17 = 40 total pizzas

40 x 2 = $80 in one weekend

$80 x 4 = $320 total for one month


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