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Rounding a Number - Cycle 2
| Mathematics
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Rounding a number means finding the nearest number that ends in one or more zeros.
A natural number can be rounded up or down to any place value.
For example, we can round to the hundreds place or the tens place. All the digits to the right of the rounded digit will become zeros.
Round the number 236 to the nearest ten and the nearest hundred.
Rounding to the Nearest Ten
We know that the number 236 is between 230 and 240.
Using a number line, we can determine if 236 is closer to 230 or 240.
The number 236 is closer to 240 than 230.
So, when we round 236 to the nearest ten, we get 240.
Rounding to the Nearest Hundred
We know that the number 236 is between 200 and 300.
Using a number line, we can determine if 236 is closer to 200 or 300.
The number 236 is closer to 200 than 300.
So, when we round 236 to the nearest hundred, we get 200.
Answers:
|
Number to round |
Number rounded |
Number rounded |
|---|---|---|
|
236 |
240 |
200 |
We can also round a decimal number to any place value. For example, we could round to the ones place or the tenths place. In this case, all the digits to the right of the rounded digit would become zeros.
Round 37.82 to the nearest unit and the nearest tenth.
Rounding to the Nearest Unit
We know that 37.82 is between 37 and 38.
Using a number line, we can determine if 37.82 is closer to 37 or 38.
The number 37.82 is closer to 38 than 37.
So, when we round 37.82 to the nearest unit, we get 38.
Rounding to the Nearest Tenth
We know that 37.82 is between 37.8 and 37.9.
Using a number line, we can determine if 37.82 is closer to 37.8 or 37.9.
The number 37.82 is closer to 37.8 than 37.9,
So, when we round 37.82 to the nearest tenth, we get 37.8.
Answers:
|
Number to round |
Number rounded |
Number rounded |
|---|---|---|
|
37.82 |
38 |
37.8 |
When a number is exactly halfway between 2 numbers, we always round it up to the higher number.
For example, let’s say we want to round 25 to the nearest ten. Even though 25 is as close to 20 as it is to 30, we have to round it up to 30.
Another example: We want to round 98.50 to the nearest unit. Even though 98.50 is as close to 98 as it is to 99, we have to round it up to 99.
Instead of using a number line to see which number the digit we’re rounding is closer to, we can use the following strategy.
-
Find the digit in the position you’re rounding to.
-
Look at the digit directly to the right.
If it’s 0, 1, 2, 3, or 4, the digit in the position you’re rounding to stays the same.
If it’s a 5, 6, 7, 8, or 9, add 1 to the digit in the position you’re rounding to. -
Replace any digits to the right of the rounded digit with zeros. If any digits to the right of the rounded digit come after a decimal point, you can delete them.
A concert at an outdoor stage attracted a crowd of 91 627 people.
If we round to the nearest ten thousand, approximately how many people attended the concert?
|
The digit in the ten thousands position in 91 627 is 9. |
|
The digit to the right of the 9 in 91 627 is a 1, so we know that the 9 stays the same. |
|
91 627 rounded to the nearest ten thousand is 90 000. |
Answer: Around 90 000 people went to the concert.
Approximating an Answer
Rounding can be used to approximate the answer to a calculation.
For example, to find the approximate answer to a complex addition problem, we can round the numbers before adding them up.
What is the approximate sum of 316 and 588?
Before adding the numbers, we can round them to the nearest hundred.
| 316 is between 300 and 400, but closer to 300, so we know that 316 rounded to the nearest hundred is 300. |
| 588 is between 500 and 600, but closer to 600, so we know that 588 rounded to the nearest hundred is 600. |
| 316 + 588 ↓ ↓ 300 + 600 = 900 |
Answer: The sum of 316 and 588 is approximately 900.