Reteaching
Name
Multiplying by Powers of 10
3-2
You can also use patterns to multiply mentally.
Fact: 48 3 1 5 48
48 3 10 5 480
48 3 101 5 480
48 3 100 5 4,800
48 3 102 5 4,800
480 3 100 5 48,000
480 3 102 5 48,000
480 3 1,000 5 480,000
480 3 103 5 480,000
Pattern: Notice that the product is always the digits 48 followed
by the total number of zeros that are in the factors.
Find 30 3 3 3 50.
Use the Commutative and Associative Properties of Multiplication
to regroup.
(30 3 50) 3 3
1,500 3 3 5 4,500
Commutative Property of
Multiplication
You can multiply factors in any
order.
15 3 9 5 9 3 15
Associative Property of
Multiplication
You can change the grouping of
factors.
(8 3 20) 3 5 5 8 3 (20 3 5)
Find each product. Use patterns and properties to compute
mentally.
1. 80 3 90 5
3. 5 3 101 3 20 5
2. 40 3 8 3 102 5
4. 4 3 30 3 25 5
5. You know that 6 3 7 5 42. How can you find 60 3 700?
R 3•2
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Practice
Name
3-2
Multiplying by Powers of 10
Use mental math to find each product.
1. 100 3 20 5
2. 0 3 50 3 800 5
3. 500 3 40 5
4. 120 3 50 5
5. 60 3 70 3 101 5
6. 9,000 3 80 5
7. 102 3 10 3 15
8. 1,800 3 20 3 0 5
9. 30 3 20 5
10. 1,400 3 2,000 5
11. 7,000 3 50 3 1 5
12. 103 3 200 3 30 5
13. A googol is a large number that is the digit one followed by one hundred
zeros. If you multiply a googol by 100, how many zeros will that product
have?
14. Gregorios drives 200 miles per day for 10 days. How many miles did he drive
in all?
15. If a 3 b 3 c 5 0, and a and b are integers greater than 10, what
must c equal?
A 0
B 1
C 2
D 10
16. SungHee empties her piggy bank and finds that she has 200 quarters,
150 dimes, and 300 pennies. How much money does she have? Explain.
P 3•2
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