Reteaching
Name
5-2
Multiplying by Multiples
of 10 and 100
Patterns can help you multiply by numbers that are multiples
of 10 or 100.
3 × 5 = 15
2 × 4 = 8
5 × 7 = 35
3 × 50 = 150
2 × 40 = 80
5 × 70 = 350
3 × 500 = 1,500
2 × 400 = 800
5 × 700 = 3,500
To find each of the products above, first complete the basic
multiplication fact. Then write the same number of zeros seen in
the factor that is a multiple of 10. If the product ends in a zero,
the answer will have an extra zero. For example:
Find 4 × 500.
First find 4 × 5.
4 3 5 5 20
Then, count the number of zeros
in the multiple of 100.
500 has 2 zeros.
Write 2 zeros after the product
of the basic multiplication fact.
So, there are 3 zeros in the product. 2,000
Find each product. Use mental math.
1. 8 × 80 =
3. 7 × 90 =
5. 3 × 40 =
7. 500 × 6 =
9. 3 × 800 =
640
630
120
3,000
2,400
2. 6 × 60 =
360
1,000
1,400
5,400
4,200
4. 5 × 200 =
6. 7 × 200 =
8. 600 × 9­=
10. 600 × 7­=
11. Number Sense To find 8 × 600, multiply 8 and 6, then
write
2
zeros to form the product.
R 5•2
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