Unit 1: Number Sense
Topic D: 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 costs $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 Hundred
A number rounded to the nearest hundred will have zeros in the ones place and in the tens place. The number will end with 000, 100, 200, 300, 400, 500, 600, 700, 800, or 900.
When rounding to the nearest 100, we are looking for the closest group of 100.
Example: 200, 220 and 300.
200
220300
Is 220 closer to 200 or 300? It is closer to 200.
Which gives a better estimate of 220 … 2 hundreds or 3 hundreds? 2 hundreds
If we round 220 to nearest hundred, the result would be 200.
Remember: The rounded number has zeroes in the tens and ones places.
Example: 300, 348 and 400.
300
348
400
Is 348 closer to 300 or 400? It is closest to 300.
Which gives a better estimate of 348 ….3 hundreds or 4 hundreds? 3 hundreds
If we round 348 to the nearest 100, the result would be 300.
Remember: The rounded number has zeroes in the tens and ones places.
Example: 600, 650 and 700
600
650
700
Is 650 closer to 600 or 700? It is closer to 700.
Which gives a better estimate of 650….. 6 hundreds or 7 hundreds? 7 hundreds. If we round 650 to the nearest hundred, the result would be 700.
When we round a number which has a 5 in the tens place, we always round up to the next hundred.
If we round 650 to nearest hundred, the result would be 700.
Example: Round 584 to the nearest 100.
584 is between 5 hundreds and 6 hundreds.
584 is closer to 6 hundreds.
Rounded number is 600.
Exercise One
Round each number to the nearest 100. Check your work using the answer key at the end of the exercise.
- 232 is between hundreds and hundreds.
232 is closest to hundreds.
Rounded number is . - 647 is between hundreds and hundreds.
647 is closest to hundreds.
Rounded number is . - 881 is between hundreds and hundreds.
881 is closest to hundreds.
Rounded number is . - 152 is between hundreds and hundreds.
152 is closest to hundreds.
Rounded number is . - 326 is between hundreds and hundreds.
326 is closest to hundreds.
Rounded number is .
| Number | Closer to ___ hundreds | Rounded Number | |
|---|---|