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How to Use the “Compensation” Strategy to Multiply Dawn Galente, Arlington CSD 2012 This is a self-paced tutorial. Click the mouse each time you want to see the next step. Click to Start

Click anywhere on slide to advance The “compensation” strategy can help us multiply numbers because it’s easier to multiply by tens. EXAMPLE: 4 x 9 = ? Step 1: Pick a factor that is close to a ten. Here we’ll use 9. + 1 9 4 Step 2: Add to EACH GROUP to make groups of ten. (We now have 4 groups of ten instead of 4 groups of 9) + 1 + 1 + 1 Step 3: Multiply the new numbers. 10 Step 4: Adjust the answer to “compensate” for the addition of 1 cube TO EACH GROUP. 4 x 10 = 40 40 – 4 = 36 I added 1 to each of 4 groups, so I subtract 4. Click anywhere on slide to advance 4 x 10 = 40

+ 2 + 2 + 2 EXAMPLE 2: 18 x 3 = Step 1: Pick a factor that is close to a ten. Add to that number to reach a ten. (In this case we will add 2 to 18 to get 20). Step 2: Multiply the new numbers. 20 x 3 = 60 Step 3: Adjust the answer to “compensate” for the addition of 2 to EACH group. Hmm, I added 2 to EACH group, so now I need to subtract 2 from EACH group. + 2 18 x 3 20 x 3 = 60 60 - 6 = 54

Example 3: 37 x 12 = Step 1: Pick an addend that is close to a ten. (We’ll use 37). Step 2: Add to that number to reach a ten. (In this case we add 3 to 37 to get 40 in EACH of the 12 groups). Step 3: Multiply the new numbers. Step 4: Adjust the answer to “compensate” for the addition of 3 to EACH group. Hmm, I added 3 to EACH group so I need to subtract 3 from EACH group. + 3 37 x 12 = 40 x 12 = 480 480 - 36 = 444

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