Lesson Video: Estimating Multiplication Products Mathematics • 5th Grade

In this video, we will learn how to use rounding and compatible numbers to estimate the product of a decimal and a whole number.

03:27

Video Transcript

Estimating Multiplication Products

In this video, we will learn how to estimate the products of two numbers including decimals by first rounding. Let’s practice with an example question. We can estimate products by rounding each number to its greatest place value as in the example.

Estimate 267 multiplied by 0.19.

Step one, identify the greatest place value in each number. The greatest place value in the number 267 is the two, worth two hundreds. And the greatest place value in 0.19 is the one, which is worth one tenth. Step two, round and multiply, 267 rounded to the nearest hundred is 300. 0.19 rounded to the nearest tenth is 0.2. 300 multiplied by 0.2 equals 60. Use this method to estimate the following products, 86 multiplied by 0.328; 717 multiplied by 0.901.

Let’s start with 86 multiplied by 0.328. Step one, we need to identify the greatest place value in each number. The greatest place value in 86 is the digit eight, which is worth eight tens. So we need to round 86 to the nearest ten. And the digit with the greatest value in 0.328 is the three, which is worth three tenths. So we’re rounding this number to the nearest tenth. 86 rounded to the nearest ten is 90. And 0.328 rounded to the nearest tenth is 0.3.

Now, we’ve rounded. We can multiply, 90 by 0.3 which equals 27. Next, we need to calculate 717 multiplied by 0.901. First, we identify the digit with the greatest place value in 717, that’s the seven, which is worth seven hundredths. And in 0.901, the greatest place value digit is the nine, which is worth nine tenths. So we’re rounding to the nearest hundred and to the nearest tenths.

717 to the nearest hundred is 700. And 0.901 to the nearest tenth is 0.9. 700 multiplied by 0.9 equals 630.

In this video, we’ve learned how to estimate the product of two numbers including decimals by, first, identifying the digit with the greatest place value in each number, then rounding and multiplying.

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