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Algebra 1

8.8.1 Evaluating Expressions Using Mental Math

Algebra 18.8.1 Evaluating Expressions Using Mental Math

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Warm Up

Finding a product mentally can be done by changing the way you look at a multiplication problem.

For example, 9·399·39 can be thought of as 9·(401)9·(401). For some people, this might be easier to calculate mentally since you can imagine the solution as 36093609, or 351. This method leverages the distributive property of multiplication over addition.

For the following questions, find each product mentally. Then, explain how you changed the way you looked at each multiplication problem to use the distributive property.

1.

9 · 11 9 · 11

2.

19 · 21 19 · 21

3.

99 · 101 99 · 101

4.

109 · 101 109 · 101

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