Grade by Grade
B. Number · Number Sense: Numbers to 100 000, Fractions, Decimals and Percents

Rounding Decimals to the Nearest Tenth

B1.6About 35 minutes
Learning goals
  • I can find the two tenths a decimal is between.
  • I can round a decimal with hundredths to the nearest tenth.
  • I can round a decimal that is exactly halfway.
  • I can use rounding with measurements and money.

Words to know

round
Change a number to a nearby, simpler number.
nearest tenth
The closest number with only one decimal place, like 2.4 for 2.37.
halfway
Exactly in the middle. 2.35 is halfway between 2.3 and 2.4.

Remember from Grade 4

In Grade 4 you rounded decimal tenths to the nearest whole number: 3.7 rounds to 4, and 3.2 rounds to 3. When a number was exactly halfway, like 3.5, you rounded up to 4. This year you'll round numbers with hundredths to the nearest tenth.

Let's start with the rain gauge

After a storm, the rain gauge at school shows 2.37 cm of rain. The weather reporter only uses one decimal place. What should she say?

2.37 is between 2.3 and 2.4. It is closer to 2.4. So she says "about 2.4 cm of rain".

2.32.352.42.37
A number line from 2.3 to 2.4 with a tick for each hundredth. The halfway point is 2.35. 2.37 is past halfway, so it rounds to 2.4.

How to round to the nearest tenth

  1. Find the two tenths the number is between. (2.37 is between 2.3 and 2.4.)
  2. The halfway point has a 5 in the hundredths place (2.35).
  3. Look at the hundredths digit:
  • 0 to 4: round down (keep the tenths digit).
  • 5 to 9: round up (add 1 to the tenths digit).

Halfway numbers (like 2.35) round up.

NumberBetweenHundredths digitRounded to the nearest tenth
2.372.3 and 2.47 (up)2.4
5.425.4 and 5.52 (down)5.4
0.050.0 and 0.15 (up)0.1
6.956.9 and 7.05 (up)7.0
Always check which tenths the number is between before deciding.
Worked example

Example 1: Round down

Round 5.42 to the nearest tenth.

  1. 5.42 is between 5.4 and 5.5.
  2. The hundredths digit is 2. That's less than 5, so round down.

5.4

Worked example

Example 2: Exactly halfway

Round 4.05 to the nearest tenth.

  1. 4.05 is between 4.0 and 4.1.
  2. The hundredths digit is 5. It's exactly halfway, so round up.

4.1

Worked example

Example 3: Rounding up to a new whole

Round 6.95 to the nearest tenth.

  1. 6.95 is between 6.9 and the next tenth, which is 7.0.
  2. The hundredths digit is 5: round up.

7.0. We write the 0 to show we rounded to the nearest tenth.

6.96.957.0halfway rounds uphalfway
6.95 sits exactly halfway between 6.9 and 7.0. Halfway numbers round up, so 6.95 rounds to 7.0, the next whole number.
Worked example

Example 4: Money

A granola bar costs $1.68. Round to the nearest tenth of a dollar (the nearest 10 cents).

  1. $1.68 is between $1.60 and $1.70.
  2. The hundredths (cents) digit is 8: round up.

About $1.70

Which digit decides?

Look at the digit just to the right of the place you are rounding to. To round to the nearest tenth, look at the hundredths. (In Grade 4, to round to the nearest whole number, you looked at the tenths.)

Just for fun

What does a number do when it's exactly halfway and can't decide?

It rounds up. Halfway numbers always look on the bright side!

Hands-on activity

Round the measurements

You need: a measuring tape or metre stick, paper and a pencil.

  1. Measure 6 things at home in centimetres: a spoon, a pencil, your foot, a pillow, a chair seat's height and a door's width.
  2. Write each length in metres with two decimal places. For example, 17 cm = 0.17 m.
  3. Round each length to the nearest tenth of a metre. For example, 0.17 m rounds to 0.2 m.
  4. Which things rounded up? Which rounded down? Did any land exactly halfway (like 0.25 m)?
  5. Bonus: look at prices in a flyer. Round 5 prices to the nearest 10 cents.

Your turn

1

Round 4.23 to the nearest tenth.

2

Round 4.28 to the nearest tenth.

3

Round 0.65 to the nearest tenth.

4

Round 9.91 to the nearest tenth.

5

Round 3.98 to the nearest tenth.

6

Round 12.04 to the nearest tenth.

7

It rained 1.46 cm. About how much is that, to the nearest tenth?

More practice: warm-up

1

Round 1.31 to the nearest tenth.

2

Round 1.39 to the nearest tenth.

3

Round 2.50 to the nearest tenth.

4

What number is halfway between 0.6 and 0.7?

5

Round 7.15 to the nearest tenth.

More practice: on your own

1

Round 8.96 to the nearest tenth.

2

Round $5.43 to the nearest 10 cents.

3

Ali rounded 3.45 to 3.4. Is he right?

4

Which of these round to 6.3: 6.25, 6.35, 6.34, 6.24?

5

The snow is 10.03 cm deep. Round to the nearest tenth.

Challenge

1

What is the least and the greatest number with two decimal places that rounds to 4.7?

2

Round 0.97 to the nearest tenth and to the nearest whole number.

3

Two runners' times both round to 9.9 s. Could their times be different? Give an example.

Check your understanding

Quiz

1.

Round 3.62 to the nearest tenth.

2.

Round 7.86 to the nearest tenth.

3.

Round 2.45 to the nearest tenth.

4.

Round 5.97 to the nearest tenth.

5.

To round to the nearest tenth, which digit do you look at?

6.

Which number rounds to 1.2?

For parents and teachers

Big idea: B1.6 asks Grade 5 students to round decimal numbers to the nearest tenth, in various contexts. A number line between two tenths, split into hundredths, makes the idea visible.

Common difficulties:

  • Looking at the wrong digit (using the tenths digit instead of the hundredths digit).
  • Rounding 6.95 to 6.10 instead of 7.0. When the tenths digit is 9 and you round up, it carries into the ones.
  • Dropping the zero (writing 7 instead of 7.0). Both have the same value, but 7.0 shows the number was rounded to tenths.

How to help: Round prices to the nearest 10 cents at the store, and measurements to the nearest tenth of a metre. Ask, "Which two tenths is it between? Which is closer?"