3.4 Rounding DecimalsOctober 1, 2010

For you notebook (copy this):

Rounding Decimals: to round a decimal to a given place value, look at the digit in the place to the right.

If the digit is 4 or less, round down.

If the digit is 5 or greater, round up.

EXAMPLE 1 Using a Number Line to Round

Use a number line to round 3.87 to the nearest tenth.

EXAMPLE 1 Using a Number Line to Round

Use a number line to round 3.87 to the nearest tenth.

EXAMPLE 1 Using a Number Line to Round

Use a number line to round 3.87 to the nearest tenth.

ANSWER

EXAMPLE 1 Using a Number Line to Round

Use a number line to round 3.87 to the nearest tenth.

The decimal 3.87 rounds up to 3.9.

ANSWER

GUIDED PRACTICE for Example 1

GUIDED PRACTICE

Use a number line to round the decimal as specified.

for Example 1

GUIDED PRACTICE

Use a number line to round the decimal as specified.

1. 1.3 (nearest one)

for Example 1

GUIDED PRACTICE

Use a number line to round the decimal as specified.

1. 1.3 (nearest one)

for Example 1

1 1. 1 1. 2 1. 3 1. 4 1. 5 1. 6 1. 7 1. 8 1.9 2.0

GUIDED PRACTICE

Use a number line to round the decimal as specified.

1. 1.3

The decimal 1.3 is closer to 1 than to 3

GUIDED PRACTICE

(nearest one)

for Example 1

1 1. 1 1. 2 1. 3 1. 4 1. 5 1. 6 1. 7 1. 8 1.9 2.0

GUIDED PRACTICE

ANSWER

The decimal 1.3 rounds down to 1.

GUIDED PRACTICE for Example 1

Use a number line to round the decimal as specified.

1. 1.3 (nearest one)

The decimal 1.3 is closer to 1 than to 3

1 1. 1 1. 2 1. 3 1. 4 1. 5 1. 6 1. 7 1. 8 1.9 2.0

GUIDED PRACTICE

Use a number line to round the decimal as specified.

for Example 1

2. 2.8 (nearest one)

GUIDED PRACTICE

Use a number line to round the decimal as specified.

for Example 1

2. 2.8 (nearest one)

2.2 2.3 2. 4 2. 5 2. 6 2. 7 2. 8 2. 9 3.0

GUIDED PRACTICE

The decimal 2.8 is closer to 3 than to 2

Use a number line to round the decimal as specified.

for Example 1

2. 2.8 (nearest one)

2.2 2.3 2. 4 2. 5 2. 6 2. 7 2. 8 2. 9 3.0

GUIDED PRACTICE

ANSWER

The decimal 2.8 rounds up to 3.

Use a number line to round the decimal as specified.

for Example 1

2. 2.8 (nearest one)

The decimal 2.8 is closer to 3 than to 2

2.2 2.3 2. 4 2. 5 2. 6 2. 7 2. 8 2. 9 3.0

GUIDED PRACTICE

Use a number line to round the decimal as specified.

for Example 1

3. 3.74 (nearest tenth)

GUIDED PRACTICE

3. 6 3. 7 3. 8 3. 9

Use a number line to round the decimal as specified.

hundredth

for Example 1

tenths

3. 3.74 (nearest tenth)

GUIDED PRACTICE

The decimal 3.74 is closer to 3.7 than to 3.8

Use a number line to round the decimal as specified.

for Example 1

3. 3.74 (nearest tenth)

3. 6 3. 7 3. 8 3. 9

hundredthtenths

GUIDED PRACTICE

The decimal 3.74 is closer to 3.7 than to 3.8

ANSWER

The decimal 3.74 rounds down to 3.7.

Use a number line to round the decimal as specified.

for Example 1

3. 3.74 (nearest tenth)

3. 6 3. 7 3. 8 3. 9

hundredthtenths

GUIDED PRACTICE

Use a number line to round the decimal as specified.

for Example 1

4. 3.86 (nearest tenth)

GUIDED PRACTICE

3. 6 3. 7 3. 8 3. 9 4. 0

Use a number line to round the decimal as specified.

tenths hundredth

for Example 1

4. 3.86 (nearest tenth)

GUIDED PRACTICE

The decimal 3.86 is closer to 3.9 than to 3.8

Use a number line to round the decimal as specified.

for Example 1

4. 3.86 (nearest tenth)

3. 6 3. 7 3. 8 3. 9 4. 0

tenths hundredth

GUIDED PRACTICE

The decimal 3.86 is closer to 3.9 than to 3.8

ANSWER

The decimal 3.86 rounds up to 3.9.

Use a number line to round the decimal as specified.

for Example 1

4. 3.86 (nearest tenth)

3. 6 3. 7 3. 8 3. 9 4. 0

tenths hundredth

Rounding Decimals (write these

examples in your notebook.)Round the decimal to the place value of the yellow

digit.

3.23 ------> 3.2, The digit to the right of 2 is 3, so round down.

6.485 ------> 6.49, The digit to the right of 8 is 5, so round up.

2.83619 -----> 2. 836, The digit to the right of the 6 is 1, so round down.

5.961 -----> 6.0, The digit to the right of 9 is 6, so round up. This causes the 5 to become a 6.

Now you try:

Round to the decimal as specified:

5.29 (nearest tenth)

7.096 (nearest hundredth)

6.48 (nearest one)

3.9876 (nearest thousandth)

Check your answers:

Round to the decimal as specified:

5.29 (nearest tenth) 5.3

7.096 (nearest hundredth) 7.10

6.48 (nearest one) 6

3.9876 (nearest thousandth) 3.988

Write this in your notebook:

Rounding Small Numbers: You can round a very small number to the place value of its leading digit to help make it easier to understand. In a decimal, the leading digit is the first nonzero digit as you read from left to right.

Rounding to the Leading Digit (you do not need to

copy this) A guitar was created that is 0.0003937 inch long.

Round the length of the guitar to the place value of the leading digit.

To Solve: The first nonzero digit as you read 0.0003937 from left to right is 3 and it is in the ten-thousandths place.

You should round the digit to the nearest ten thousandth. Because 9 is to the right of the ten-thousandth’s place, round 3 up to 4.

Answer the length rounded to the leading digit is 0.0004 inch.

Try these (in your notebook)

Round the decimal to the leading digit

0.058

0.0091

0.0952

0.006192

Check your answers.

Round the decimal to the leading digit

0.058 0.06

0.0091 0.009

0.0952 0.10 (you don’t have to have the last 0)

0.006192 0.006

When you finish this slideshow:

Take the section quiz (as practice) on classzone.com. Go to assessments, then click on section quizzes. Then click on 3.4 Rounding Decimals.

Then play the animated math game on classzone.com. Go to animated math. Then click on Chapter 3: Comparing, Ordering and Rounding Decimals.