Rounding a Number | Elementary

Rounding a Number - Cycle 1

| Mathematics

Definition

Rounding a number means finding the nearest number that ends in one or more zeros.

We can round to the nearest ten or the nearest hundred.

Example

Round the number 236 to the nearest ten and the nearest hundred.

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.

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 to the nearest ten	Number rounded to the nearest hundred
236	240	200

Be careful!

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 350 to the nearest hundred. Even though 350 is as close to 300 as it is to 400, we have to round it up to 400.

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.

Example

What is the approximate sum of 57 and 34?

Before adding the numbers, we can round them to the nearest ten.

Round 57 to the nearest ten.	57 is between 50 and 60, but closer to 60, so we know that 57 rounded to the nearest ten is 60.
Round 34 to the nearest ten.	34 is between 30 and 40, but closer to 30, so we know that 34 rounded to the nearest ten is 30.
Add the 2 rounded numbers.	57 + 34 ↓ ↓ 60 + 30 = 90

Answer: The sum of 57 and 34 is approximately 90.