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Multiplying by 10 and 100
Estimating
Breaking Apart
Turning Addition Into Multiplication
Is the Answer Reasonable?
100
100 x 30
3,000
100
Estimate the Product 54 x 3 =
50 x 3 = 150
100
Break Apart to Find the Product. 54 x 6 =
(50 x 6) + (4 x 6) = 324
100
6 + 6 + 6 + 6 + 6
6 x 5 = 30
100
Is 20 a reasonable answer for 200 x 3?
No, because 200 x 3 = 600 and the two are not close.
200
20 x 4
80
200
Estimate the Product 86 x 9 =
90 x 9 = 810
200
Break Apart to Find the Product 67 x 3
(60 x 3) + (7 x 3) = 201
200
10 + 10 + 10 + 10 + 10 + 10
10 x 6 = 60
200
Is 40 a reasonable answer for 24 x 2?
Yes, because 24 x 2 is 48 and the two are close.
300
6,000 x 5
30,000
300
Estimate the Product 71 x 2 =
70 x 2 = 140
300
Break Apart to Find the Answer 48 x 2 =
(40 x 2) + (8 x 2) = 96
300
3 + 3 + 3
3 x 3 = 9
300
Is 300 a reasonable answer for 154 x 2?
Yes, because 154 x 2 = 308 and the two are close.
400
300 x 200
60,000
400
Estimate the Product 187 x 4 =
200 x 4 = 800
400
Break Apart to Find the Answer 98 x 9 =
(90 x 9) + (8 x 9) = 882
400
5 + 5 + 5 + 5 + 5 + 5 + 5 + 5 + 5
5 x 9 = 45
400
Is 1,000 a reasonable answer for 10 x 10?
No, because 10 x 10 = 100 and the two are not close.
500
9,000 x 90
810,000
500
Estimate the Product 456 x 7 =
500 x 7 = 3,500
500
Break Apart to Find the Answer 112 x 4 =
(100 x 4) + (10 x 4) + (2 x 4) = 448
500
20 + 20 + 20
20 x 3 = 60
500
Maria knows there are 24 hours in one day and 7 days in one week. So, she figured out that there are 168 hours in one week. Is her answer reasonable? Explain why or why not.
Yes, her answer is reasonable because 24 x 7 = 168, also 24 x 7 estimated is 20 x 7 = 140 and the two are close.