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3rd-5th Grade Math: Practice & Review37 chapters | 251 lessons

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Instructor:
*Dana Sparkman*

In multiplication problems, sometimes we want to get an answer that is 'close enough,' not exact. In this lesson, you will learn how to estimate products to get a 'close enough' answer.

There are two skills needed for estimating products: rounding and multiplying with zeroes. Let's take a closer look at these skills now.

When we **round** numbers, we adjust them so that they are more 'friendly,' or easier to use when calculating.

We can round to the nearest ten, the nearest hundred, and so on. When rounding to the nearest ten, for example, look at the number to the right of the tens place. If it is 5 or greater, raise the number in the tens place by one digit, and change the number in the ones place to zero. If it is less than 5, leave the number in the tens place as it is, and change the number in the ones place to zero.

**Example 1:** 78

The number to the right of the tens place is 8. Because 8 is greater than 5, raise the number in the tens place - 7 - up to 8, and change the number in the ones place to zero. So, 78 rounds to 80.

**Example 2:** 437

Here, we will round to the nearest hundred. Look at the number to the right of the hundreds place (in this case, 3). Because 3 is less than 5, keep the number in the hundreds place at 4, and change the other digits to zeroes. So, 437 rounds to 400.

To multiply numbers with zeroes, first multiply the non-zero numbers together. Then, write the number of zeroes you see in the problem on the end of the answer.

**Example 1:** 80 x 30

Multiply the non-zero numbers: 8 x 3 = 24

Write the number of zeroes you see on the end of the answer. Here, there are two zeroes, so the answer becomes 2,400.

**Example 2:** 40 x 700

Multiply the non-zero numbers: 4 x 7 = 28

Write the number of zeroes you see on the end of the answer. Here, there are three zeroes, so the answer becomes 28,000.

**Step 1:** Round 2 and 3 digit numbers to the nearest ten or hundred. Do not round one-digit numbers.

**Step 2:** Multiply the non-zero digits.

**Step 3:** Write the number of zeroes in the rounded numbers on the end of the answer.

7 x 58 = ?

7 is a one-digit number, so do not round.

Round 58 to the nearest ten. Because the number in the ones place is five or greater, round up to 60.

7 x 60 = ?

Multiply the non-zero digits: 7 x 6 = 42

Write the number of zeroes you see (just one zero).

Answer: 420

4 x 325 = ?

4 is a one-digit number, so do not round.

Round 325 to the nearest hundred. Because the number in the tens place is less than five, round down to 300.

4 x 300 = ?

Multiply the non-zero digits: 4 x 3 = 12

Write the number of zeroes you see (two of them).

Answer: 1,200

38 x 62 = ?

First, round the numbers. These are 2-digit numbers, so round to the nearest ten.

38 rounds to 40, and 62 rounds to 60.

The problem becomes: 40 x 60 = ?

Multiply the non-zero digits: 4 x 6 = 24

Write the number of zeroes you see (two of them).

Answer: 2,400

If you want to estimate products in multiplication problems, there are two skills you need. First, you need to **round**, or adjust, numbers so they are easier to use. Second, you need to multiply with zeroes by multiplying the non-zero numbers first, then adding on the number of zeroes in the problem to the end of your answer.

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3rd-5th Grade Math: Practice & Review37 chapters | 251 lessons

- How to Round Whole Numbers 6:03
- Rounding Numbers to the Nearest 1000, 10,000 & 100,000 7:04
- Estimating a Difference by Rounding 4:57
- How to Use Front-End Estimation 5:26
- Rounding Decimals & Finding the Missing Digit 6:50
- Estimating the Sum & Difference Between Two Decimals 5:12
- How to Round Mixed Numbers 3:20
- How to Estimate Products
- How to Solve Inequalities Using Estimation 7:40
- Go to Estimation & Rounding

- Go to Addition

- Go to Subtraction

- Go to Division

- Go to Angles

- Go to Money

- Go to Time

- Go to Integers

- Go to Percents

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