Eight's

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Objective

Students will be able to fluently multiply with 8's.

Big Idea

Double the Doubles Doubled!

Lesson Author

Erin Doughty

Grand Rapids, MI

Grade Level

Fifth grade

Subjects

Math

Standards

3.OA.C.7

Fluently multiply and divide within 100, using strategies such as the relationship between multiplication and division (e.g., knowing that 8 × 5 = 40, one knows 40 ÷ 5 = 8) or properties of operations. By the end of Grade 3, know from memory all products of two one-digit numbers.

MP1

Make sense of problems and persevere in solving them.

Concept

15 minutes

In order to build understanding of multiplying by 8 students need to be comfortable with their 4's and the concept of doubling. 8's are just 4's doubled.

For example, 8 x 5 is the same as 4 x 5 and 4 x 5 or 20 + 20. This will be difficult for students who lack an understanding of doubling and mastery of their products using 4 as a factor.

I have included a short video for multiplying by 8. This is meant to be more of a review and practice instead of a concept introduction.

Practice

30 minutes

Spinner Tool

Students are given one of the spinners to fill out as a reference tool. The tool will be primarily used during the current level of the multiplication program but should be kept as a reference going forward to higher levels.

Flashcards

There is a set of flashcards provided for the current level. Each set of flashcards include the facts with their turn-around facts. It is important that the students are comfortable with the commutative property of multiplication.

Games for Practice

Jumbo Tic-Tac-Toe

Each player chooses one factor (2-12)
Record the factor in the top of second column
Toss 2 dice and find the sum
Multiply the sum by the factor
Record the product next to the sum in the table
If the sum has already been filled, lose a turn
First player to complete the table wins

Line It Up

Toss 2 dice and find the sum
Multiply the sum by 2
Place a counter on the product
If the product has a counter on it, lose a turn
First player to build a full row or column wins

Face-Off

Each player chooses one factor (2-12)
Record the factor in the top of second column
Toss 2 dice and find the sum
Multiply the sum by the factor
Record the product next to the sum in the table
If the sum has already been filled, lose a turn
First player to complete the table wins

Timed Test

15 minutes

Grid Reflection 8

There are two timed tests associated with this new factor. The first timed test is designed to be a one minute test of 40 problems and includes only multiplication facts with the new factor. The second timed test is designed to be a two minute test of 60 problems and includes all multiplication facts learned in the leveled program thus far.

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