Lesson 1 — Activity 4:

Estimating and Rounding Numbers


While shopping, you may need to add the cost of items you want to buy to be sure you have enough money to pay for them. Many items that you find in the store include dollars and cents.

For example:

$24.99

$32.45

$64.69

Being able to round these values to the nearest whole number makes getting the total cost (or at least an estimate of the total cost) easier!


Estimates are based on educated guesses and also on rounding. It means to roughly calculate the value, number, or quantity of something.


What is rounding?

Rounding means making a number simpler, but keeping its value close to what it was. The result is less accurate, but easier to use.

Example:

73 rounded to the nearest 10 is 70 because 73 is closer to 70 than to 80.

76 rounded to the nearest 10 is 80 because 76 is closer to 80 than to 70.



How to Round Numbers

  • Decide which is the last digit to keep (this depends on the place value you are rounding your number to).

  • Leave it the same if the next digit is less than 5 (this is called rounding down). OR

  • Increase it by 1 if the next digit is 5 or more (this is called rounding up).




Example: Round 74 to the nearest ten.

  • We want to keep the 7 (it is in the tens position).
  • The next digit is 4, which is less than 5, so no change is needed to the 7.
Answer: 70 (74 gets rounded down.)


Example: Round 86 to the nearest ten.

  • We want to keep the 8 (it is in the tens position).
  • The next digit is 6, which is 5 more, so increase the 8 by one, which is 9.
Answer: 90 (86 gets rounded up.)


What happens if the keep number is 5?

5 is in the middle, so we could go up or down. But we need a method that everyone agrees with.

So think about playing a sport — we should have the same number of players on each team, right?

  • 0, 1, 2, 3, and 4 are on "team down" (always round these numbers down).
  • 5, 6, 7, 8, and 9 are on "team up" (always round these numbers up).


Example: Round 85 to the nearest ten.


  • We want to keep the 8 (it is in the tens position).
  • The next digit is 5, which is in the middle, so increase the 8 by one, which is 9.
Answer: 90 (85 gets rounded up.)

Now let's think about the examples at the beginning of this lesson. When you go shopping, many of the items that you want to buy include dollars and cents. Rounding these numbers will help you to estimate if you have enough money to buy them.


For example:

$24.99 for a belt

$32.45 for a shirt

$64.69 for a pair of jeans


Self-check!

Try this!


Round the following numbers to the identified place value:

  • 734 to the nearest hundred
  • 8,725 to the nearest thousand
  • 35 to the nearest ten


Extra Practice!

Click here to download extra practice questions (with answers)!