Multiplying by 100 – Elementary Math

Purpose

To practice mental multiplication by 10 and 100

Materials

None

Overview

To review mental multiplication, say a number that is a multiple of 10 (a “decade” number) and have a student multiply that number by 10. For example, if your number is 60, the student would say 600. Say numbers and call on students quickly to keep the activity fast-paced. Repeat the activity, asking students to multiply by 100. To keep the pace moving, select volunteers by using a deck of cards with their names (and don’t automatically shuffle the card to the back after using) to keep them engaged and ready to share.

About the sequence

Part 1 asks students to multiply decade numbers by 10. Part 2 has students multiply any two-digit numbers by 10 or 100. The extension asks students to multiply any number by either 10, 100, or 1,000.

Part 1

Let’s see how many numbers we can multiply by 10. Here we go!

Examples:

20 × 10 (200)
40 × 10 (400)
30 × 10 (300)
60 × 10 (600)
90 × 10 (900)
80 × 10 (80)
40 × 10 (400)

Part 2

Now let’s multiply any two-digit number by either 10 or 100. For example, if I say 27 × 10, your answer is 270. If I say 32 × 100 the answer is 3,200. Here we go!

Examples:

15 × 100 (1,500)
23 × 10 (230)
17 × 10 (170)
31 × 100 (3,100)
11 × 10 (110)
92 × 10 (920)
41 × 100 (4,100)
33 × 100 (3,300)

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

Extension

Now let’s multiply any number by 10, 100 or 1,000.

4 × 1,000 (4,000)
12 × 100 (1,200)
7 × 1,000 (7,000)
23 × 100 (2,300)
67 × 100 (6,700)
11 × 10 (110)
5,400 × 100 (540,000)
120 × 1,000 (120,000)
3,333 × 1,000 (3,333,000)