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Published byAnthony Wilcox Modified over 8 years ago

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Let’s estimate when we multiply decimal fractions! This is one way to check our products.

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Find 12 x 0.48 by rounding. Round the 12 to 10 Round the 12 to 10 Round the 0.48 to.5 Round the 0.48 to.5 Now, let’s multiply. Now, let’s multiply. 10 x.5 = 5.0 10 x.5 = 5.0

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Our answer should be near 5 according to our estimation. Let’s multiply: Let’s multiply: 0.48 0.48 x 12 x 12 96 96 + 480 + 480 5.76 5.76 Since the estimate is 5, place the decimal point so there is a one-digit whole number in the product.

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Count Decimal Places Let’s multiply: Let’s multiply: 0.48 0.48 x 12 x 12 96 96 + 480 + 480 5.76 5.76 Since we had two decimal places in our factors, we have to have two places in our product.

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Let’s count decimal places, again. Find the product of 0.7 x 0.5 Find the product of 0.7 x 0.5 Multiply as you do with whole numbers. Multiply as you do with whole numbers. 0.7 0.7 x 0.5 x 0.5 0.35 0.35 Count the decimal places in each factor. There are 2 decimal places in the factors. We need 2 decimal places in the product.

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Your turn. Estimate by rounding. Estimate by rounding. 0.4 x 1.7 = What should you do first?

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Estimation Let’s round 0.4 to 0.5 Let’s round 0.4 to 0.5 Next, round 1.7 to 2 Next, round 1.7 to 2 Now, let’s multiply. Now, let’s multiply. 0.5 x 2 = 1.0 0.5 x 2 = 1.0 Let’s check our answer. It should be near 1.

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Count the decimal places to multiply. Multiply: Multiply:.4.4 x 1.7 x 1.7 28 28 40 40.68.68 There are 2 decimal places in our factors. We have to have 2 decimal places in our product..68 would round to 1.0

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Your turn again. How many decimal places will be in the product for these factors? How many decimal places will be in the product for these factors? 2.5 x.07 2.5 x.07 Count.5 and.07 Count.5 and.07 There will be 3 decimal places in the product. There will be 3 decimal places in the product.

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