Common Factors – Elementary Math

Purpose

To identify common factors between two numbers

Materials

None

Overview

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.

About the sequence

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.

Part 1

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.

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)