Grade: 5, Topic(s): multiplication/division

## Purpose

To identify common factors between two numbers

None

Tell students that you will say two numbers and students are to reply with a factor that the two numbers have in common. The factor 1 can be given as a response *only *if that is the pair’s only common factor. This might be a good time to use a deck of student name cards to keep the pace moving and to encourage all students to prepare to answer.

Part 1 asks students to identify common factors of 2 numbers, both less than 50. Part 2 offers more practice identifying common factors of 2 numbers less than 100.

I’ll share two numbers – what is a factor that they have in common? 1 can only be used if it’s the only common factor.

Examples:

- 4 and 8 (2, 4)
- 12 and 6 (2, 3, 6)
- 28 and 4 (2, 4)
- 5 and 15 (5)
- 6 and 30 (2, 3, 6)
- 6 and 9 (3)

*While children are enjoying their building of mastery, feel free to repeat. When children are eager for more, try Part 2.*

Let’s keep looking for more factors that a pair of numbers have in common! (Offer pairs of numbers less than 100.)

Examples:

- 40 and 50 (2, 5, 10)
- 39 and 42 (3)
- 42 and 56 (2, 7, 14)
- 21 and 63 (3, 7, 21)
- 30 and 90 (2, 3, 5, 6, 10, 15, 30)
- 45 and 75 (3, 5, 15)
- 60 and 30 (2, 3, 5, 6, 10, 15, 30)

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