Unit 1: Number Sense

Topic E: Rounding Numbers

We use numbers a lot in our everyday lives. List some of the ways you use numbers.

                                                                                               
                                                                                               
                                                                                               

You may have written money, shopping, time, and counting as part of your answer.

Think about time. Let’s say it takes eight minutes to walk to the bus. If someone asks you how long it takes, you will probably say, “About ten minutes.”

If you buy a sweater that cost $29, you may say, “Oh, it was around thirty dollars.”

How far is it from Vancouver to Prince George? The map says 796 km, but we would probably say, “About 800 kilometres.”

You have just read examples of rounding numbers.

We round numbers for many reasons:

  • We may not know the exact number.
  • The exact number may not be important for what we are doing.
  • We may need a quick way to figure something out.

When you are rounding numbers, use zeros to hold the places at the end of the number. Work through the following examples and exercises carefully. Rounding is an important skill.

Rounding to the Nearest Ten

Here is a short method to round to the nearest ten. When rounding to the nearest ten, do this:

  1. Underline the tens digit. 83
  2. Look at the digit following in the ones place. 83
  3. If the digit in the ones place is less than 5, write a 0 in the ones place. Leave the tens digit as it is.
    • 42, rounds to 40 (42 is nearer to 40 than to 50)
    • 14, rounds to 10
    • 83, rounds to 80
  4. If the digit in the ones place is 5 or more, write a 0 in the ones place. Add one more ten to the tens place.
    • 36, rounds to 40 (36 is nearer to 40 than to 30)
    • 25, rounds to 30
    • 98, rounds to 100 (one more ten than nine tens is ten tens)

Note: If you are rounding to the nearest ten, single digits are rounded like this:

  • 0, 1, 2, 3, 4 all round to 0.
  • 5, 6, 7, 8, 9 all round to 10.

A number rounded to the nearest ten will have a zero in the ones place.

The number will end with

0, 10, 20, 30, 40, 50, 60, 70, 80, or 90.

When you round a number, use the sign that means “approximately equal” ≈.

Exercise 1

Round each number to the nearest 10. Check your work using the answer key at the end of the exercise.

  1. 47 is between           tens and           tens.
    47 is closest to           tens.
    Rounded number is          .
  2. 81 is between           tens and           tens.
    81 is closest to           tens.
    Rounded number is          .
  3. 14 is between           tens and           tens.
    14 is closest to           tens.
    Rounded number is          .
  4. 26 is between           tens and           tens.
    26 is closest to           tens.
    Rounded number is          .
  5. 98 is between           tens and           tens.
    98 is closest to           tens.
    Rounded number is          .
  6. 57 is between           tens and           tens.
    57 is closest to           tens.
    Rounded number is          .
  7. 73 is between           tens and           tens.
    73 is closest to           tens.
    Rounded number is          .

Answers to Exercise 1

  1. 4 tens, 5 tens
    5 tens
    50
  2. 8 tens, 9 tens
    8 tens
    80
  3. 1 tens, 2 tens
    1 ten
    10
  4. 2 tens, 3 tens
    3 tens
    30
  5. 9 tens. 10 tens
    10 tens
    100
  6. 5 tens, 6 tens
    6 tens
    60
  7. 7 tens, 8 tens
    7 tens
    70

Exercise 2

Round each number to the nearest ten. Check your work using the answer key at the end of the exercise.

  1. 22 ≈    20   
  2. 86 ≈    90   
  3. 31 ≈          
  4. 96 ≈          
  5. 84 ≈          
  6. 55 ≈          
  7. 8 ≈          
  8. 2 ≈          
  9. 63 ≈          
  10. 49 ≈          
  11. 25 ≈          
  12. 71 ≈          
  13. 38 ≈          
  14. 51 ≈          
  15. 88 ≈          

Answers to Exercise 2

  1. 30
  2. 100
  3. 80
  4. 60
  5. 10
  6. 0
  7. 60
  8. 50
  9. 30
  10. 70
  11. 40
  12. 50
  13. 90

Numbers of any size can be rounded to the nearest ten using the method you have just learned.

[latex]\large \begin{array}{rll} \downarrow && \\ 2\underline{3}8 & \approx & 240 \end{array} \qquad \begin{array}{rll} \downarrow && \\ 8\underline{8}3 & \approx & 880 \end{array}\qquad \begin{array}{rll} \downarrow && \\ 2\underline{9}8 & \approx & 300 \end{array}[/latex]

Exercise 3

Round each number to the nearest ten. Check your work using the answer key at the end of the exercise.

  1. 424 ≈          
  2. 867 ≈          
  3. 499 ≈          
  4. 132 ≈          
  5. 278 ≈          
  6. 617 ≈          
  7. 208 ≈          
  8. 851 ≈          
  9. 124 ≈          
  10. 576 ≈          
  11. 315 ≈          
  12. 742 ≈          
  13. 397 ≈          
  14. 952 ≈          
  15. 639 ≈          

Answers to Exercise 3

  1. 420
  2. 870
  3. 500
  4. 130
  5. 280
  6. 620
  7. 210
  8. 850
  9. 120
  10. 580
  11. 320
  12. 740
  13. 400
  14. 950
  15. 640

Exercise 4

For each problem, round the numbers to the nearest ten. Check your work using the answer key at the end of the exercise.

Example: 

Mei Ling has just moved into a new apartment. She bought the following items. Round each amount to the nearest ten.

Item Cost Rounded to nearest ten
Towels $14 $10
Dishes $32 $30
Saucepan $43 $40
Microwave $109 $110
Carving knife $18 $20
  1. Akkul walked 12 kilometres on Monday, 26 kilometres on Tuesday and 6 kilometres on Wednesday. Round each number to the nearest ten.
    Day Number Rounded Number
    Monday 12  
    Tuesday 26  
    Wednesday 6  
  2. Werner is a keen bird watcher. On Monday, he saw 57 birds, on Tuesday he saw 124 birds, on Wednesday he saw 31 birds and on Thursday he saw 75 birds. Round each number to the nearest ten.
    Day Number Rounded Number
    Monday 57  
    Tuesday 124  
    Wednesday 31  
    Thursday 75  
  3. Jamir drove 678 kilometres, 493 kilometres, 387 kilometres and 914 kilometres in one week. Round each mileage to the nearest ten.
    Day Kilometres Rounded Number
    #1 678  
    #2 493  
    #3 387  
    #4 914  

Answers to Exercise 4

  1. 10, 30, 10
  2. 60, 120, 30, 80
  3. 680, 490, 390, 910

Topic E Self-Test

Mark     /12          Aim      10/12

  1. Round your answer to the nearest ten. (8 marks)
    1. 47 ≈          
    2. 123 ≈          
    3. 4 ≈          
    4. 945 ≈          
    5. 329 ≈          
    6. 481 ≈          
    7. 865 ≈          
    8. 916 ≈          
  2. Round each number to the nearest ten. (4 marks)
    Mary scored 78, 91, 79, 67 and 102 on her arithmetic test. Round her scores to the nearest ten.
    Score Rounded Score
    78  
    91  
    79  
    67  
    102  

Answers to Topic E Self-Test

    1. 50
    2. 120
    3. 0
    4. 950
    5. 330
    6. 480
    7. 870
    8. 920
    1. 80, 90, 80, 70, 100

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Adult Literacy Fundamentals Mathematics: Book 1 - 2nd Edition by Wendy Tagami and Liz Girard is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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