Multiplying by Multiples of 10

Purpose

To multiply numbers by multiples of 10

Materials

None

Overview

To practice mental computation, have students multiply one-digit numbers by 10, 100, 20, 30, and 40. Keep the activity moving quickly so that all students have a chance to participate. If necessary, you might remind students that 20 is 2 x 10, 30 is 3 x 10, and 40 is 4 x 10. Students may find that breaking up 20, 30, and 40 in this way is easier than multiplying by those numbers directly.

About the sequence

Part 1 asks students to multiply one-digit numbers by 10, 100 and 20. Part 2 asks students to multiply one-digit numbers by 30 and 40 (in addition to multiplying by 10, 100 and 20). The extension multiplies two-digit numbers by 10, 100, 20, 30 and 40.

Part 1

Let’s multiply one-digit numbers by 10, 100 and 20. (If multiplying by 20 feels challenging, remember 20 is the same as 2 × 10.)

Examples:

3 × 10 (30)
3 × 100 (300)
3 × 20 (60)
2 × 10 (200)
2 × 100 (200)
2 × 20 (40)
5 × 100 (500)
5 × 10 (50)
5 × 20 (100)
7 × 100 (700)
7 × 10 (70)
7 × 20 (140)

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 multiply one-digit numbers by 30 and 40, as well as by 10, 100, 20. (Remember multiplying by 30 is 3 × 10 and 40 is 4 × 10). Here we go!

Examples:

4 × 20 (80)
4 × 30 (120)
4 × 40 (160)
4 × 100 (400)
6 × 20 (120)
6 × 30 (180)
6 × 40 (240)

As always, when children seem excited for a new challenge, move on.

Extension

Let’s multiply any two-digit numbers by 10, 20, 30, 40, and 100.

Examples:

20 × 30 (600)
60 × 40 (2,400)
70 × 20 (1,400)
90 × 40 (3,600)
40 × 100 (4,000)
50 × 10 (500)
33 × 30 (990)
87 × 100 (8,700)