Lesson 1 — Activity 1: Rounding Whole Numbers



Getting Ready


Think about what you already know about the place value of numbers. Remember that place value is the value of a number based on the place or position in that number.


Below are the place values of this number.

This image shows the place values of 1,234,567.


Try This:


Identify the place value of the underlined digit in the following numbers:

  • 3,456


  • 775,525


  • 32,194


  • 3,456: 5 is in the tens position
  • 775,525: 7 is in the ten thousands position
  • 32,194: 4 is in the ones position




In this activity, you will practise rounding whole numbers to the nearest ten, hundred, and thousand.

You will consider place value as you complete this first activity.


Have you ever watched someone who has done a lot of cooking or baking make something? Do they always use a measuring spoon for something like adding salt to the ingredients?


You may have seen your mother or grandmother just pouring a bit out of the container and saying, “That's about a teaspoon of salt” and going on with the recipe. She was just estimating the amount of salt to use.



Sometimes working with numbers is similar. You don't have to be exact; you can estimate.Think of it this way: if there were 1,000,050 people at an outdoor concert, you could say there were about a million people there.


This is known as rounding a number.

Images courtesy of www.imagesgoogle.com

Estimating, or being able to guess and come close to a correct answer, is an important part of mathematics and a very handy tool for everyday life. You should get in the habit of estimating amounts of money, lengths of time, distances, and many other physical quantities. Rounding is a kind of estimating.




Think about these examples of rounding:


  • Temperature:

             Temperatures are often estimated.

    Daily temperatures are often rounded to the nearest degree Celsius. E.g., 25.7°C is generally reported as 26°C.


  • Money:

    Costs of items are often estimated.

    People often use rounding and estimating at a store to make sure they have enough money to pay for items before they get to the cashier.      


  • Using large numbers:

    Newspapers often estimate large numbers to save space.

    Newspapers often round large numbers to take up less space.They may print $10M rather than $10,490,721.00. When adding or subtracting large numbers mentally, it is easier to round them first!

             



The following is the general process for rounding any number:


  • First, look at the number to the right of the place you wish to work with.
  • Second, if that number is 4 or less, round the number down.
  • Third, if that number is 5 or greater, round the number up.


Here's an example of the number 547 rounded to the nearest ten:


  • Find the place value to be rounded and highlight it in the digit:

    547

    (4 is in the tens place)
  • Underline the digit to the right of the highlighted number:

    547

    (7 is to the right of 4)

  • If the underlined digit is 4 or less, round down. If it is greater than 4, skip to the next step. (7 is greater than 4, so go to the next step.)


  • If the underlined digit is 5 or greater, round up. To round up, increase the highlighted number by one and change any digits to its right to zeros:

    547

    becomes

    550




Here are some further examples of rounding in everyday situations. Click on each box below.


  • Find the place value to be rounded and highlight it in the digit:

    1,237

    (2 is in the hundreds place)
  • Underline the digit to the right of the highlighted number: 

    1,237

    (3 is to the right of 2)
  • If the underlined digit is 4 or less, round down. If it is greater than 4, skip to the next step. To round down, change the underlined digit and any other digits to its right to zeros.  

    1,237

    (3 is 4 or less, so round down):

    1,237

    becomes

    1,200

  • Glen spent approximately $1,200 for his new computer.

First car: $4,253:
  • Find the place value to be rounded and highlight in the digit: 4,353 (4 is in the thousands place)
  • Underline the digit to the right of the highlighted number:

    4,253

    (2 is to the right of 4)
  • If the underlined digit is 4 or less, round down. If it is greater than 4, skip to the next step. To round down, change the underlined digit and any other digits to its right to zeroes.

    4,253

    (The highlighted number is 4 or less, so round down)

    4,253

    becomes

    4,000

    when rounded to the nearest thousand.
  • The first car costs approximately $4,000.


Second car: $8,765:
  • Find the place value to be rounded and highlight it in the digit:

    8,765

    (8 is in the thousands place)
  • Underline the digit to the right of the highlighted number:

    8,765

    (7 is to the right of 8)
  • If the highlighted digit is 4 or less, round down. If it is greater than 4, skip to the next step. (7 is greater than 4, so go to the next step.)
  • If the underlined digit is 5 or greater, round up. To round up, increase the highlighted number by one and change any digits to its right to zeroes.

    8,765

    becomes

    9,000

    when rounded to the nearest thousand.
  • The second car costs approximately $9,000.


Don't be afraid of larger numbers. You can follow the same steps as above. Here is an example of a number rounded to the nearest ten thousand:



335,400


  • Find the place value to be rounded and highlight it in the digit:

    335,400

    (3 is in the ten thousands place)
  • Underline the digit to the right of the highlighted number:

    335,400

    (5 is to the right of 3)
  • If the underlined digit is 4 or less, round down. If it is greater than 4, skip to the next step. (5 is greater than 4, so go to the next step.)
  • If the underlined digit is 5 or greater, round up. To round up, increase the highlighted number by one and change any digits to its right to zeros:

    335,400

    becomes

    340,000



You can also use a number line to round numbers. Click here to see how to do this.



Go to the next page to try a Self-check Activity on rounding numbers.