Decimal Multiplication and Division
SCMP Summer 2009
Decimal Multiplication and Division
1. Discuss how to estimate
0.3 0.2
2. Represent 0.3 0.2 in as many ways as possible. Your
representation should include the problem as well as the
answer. You may use any materials. Here are some ideas:
 Decimal grid paper
 Decimal blocks
 Using fractions
3. Now represent
above.
0.03 0.2
using the same instructions as
4. Let’s focus on teaching multiplication of decimals using the
common fraction approach. For this, students should use
their existing knowledge of fractions, performing the
fraction multiplication and writing the answer as a decimal.
Lets try this with the following problem: 0.3 0.26
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Decimal Multiplication and Division
SCMP Summer 2009
5. Decide which of the choices is closest to the product of the
2 given numbers.
0.3 x 4.2 =
a. 2.1
b. 12.6
c. 1.3
0.322 x 0.46 =
a. 1.5
b. 0.15
c. 15
1.43 x 2.3 =
a. 2.8
b. 3.2
c. 3.0
6. Use the common fraction approach to solve the following
decimal multiplication problems.
a. 0.3 x 4.2 =
b. 0.322 x 0.46 =
c. 1.43 x 2.3 =
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Decimal Multiplication and Division
SCMP Summer 2009
7. How might the common fraction approach help justify the
“traditional algorithm” for multiplying decimals?
8. Can the common fraction approach also be applied to division
of decimals? Try it with this problem: 0.6  0.2
9. Is there another approach you could use for the above
division problem?
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Decimal Multiplication and Division
SCMP Summer 2009
10.
Use the common fraction approach (or another
approach) to solve the following decimal division problems.
Before solving each problem, come up with a reasonable
estimate.
a. 3.4  2 =
b.
0.32  0.8 =
c.
4.5135  0.85 =
11. Justify the “traditional algorithm” for dividing decimals.
For example, why do we move the decimal point in the
divisor and dividend before dividing, and why are we allowed
do so?
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Decimal Multiplication and Division
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SCMP Summer 2009