Hi, my name is Grace, and welcome to Rounding 1.
In this video you'll learn to round numbers.
Rounding makes it easier to estimate the answer to a math problem in your head,
rather than on paper or with a calculator.
In this video, we'll round to the tens place.
Rounding means to express a number to the nearest given place.
Rounding makes a number easier to read and to understand.
You probably already use rounding and don't know it.
Have you ever seen something priced $1.99, and said it was $2.00?
If you have, that's rounding.
There's a pretty simple rule for rounding.
If the digit to the right of a given place value is between 5 and 9, you round up.
This means the number in a given place is increased by one
if the digit to its right is 5 or more.
If the digit to the right of the given place value is between 1 and 4, you round down.
The number in the given place remains the same
if the digit to its right is less than 5.
Let's look at some examples to see how this works.
Let's round off the number 12 to the nearest tens place.
The digit to the right of the tens place is 2.
Since we round down to the nearest tens place, 12 becomes 10.
If you remember the rounding rule,
when the digit to the right of the given place value is between 1 and 4,
or less than 5, we round down.
The place value, tens, remains the same.
And the digit that follows in the ones place, becomes 0.
In the number 17, the digit to the right of the tens place is 7.
7 is between 5 and 9, so this digit rounds up to 20.
Again, the rounding rule tells us that if the digit to the right of a given place value
is between 5 and 9, we round up to the nearest place value.
In this case the tens place increases by 1,
and the number that follows in the ones place becomes 0.
Let's try rounding in a real life situation.
You are at a store with money you received for your birthday.
You find a game at $23 and a set of novels at $36.
You want to know if you have enough money to pay for both items.
Rather than being surprised at check out,
you can roughly calculate the rough amount in your head by rounding.
These numbers round off to $20 and $40.
Here's why.
$23 rounds down because the digit to the right of the tens place is 3,
and 3 is less than 5.
The tens place remains the same, and we follow it with a 0.
$36 rounds up to the nearest tens
becausethe digit to the right of the tens place is 6,
and 6 is between 5 and 9.
The tens place increases by 1, and we follow this digit by a 0.
Add it together. That makes $60.
You know the total will be around $60.
This is also known as making and estimate,
an approximate, or close enough calculation.
Now you can decide whether you have enough money to pay for these items.
Keep in mind that rounding won't result in a precise number,
so you should not just rely on the estimate alone.
Bring some extra money just in case.
If we solve the original equation, we see that the answer is $59.
That's pretty close to your quick mental calculation, isn't it?
Heading to the check out counter, won't be much of a surprise now,
all thanks to the rule of rounding.
Rounding is actually a cool mental math trick.
When you can use your head to solve a math problem,
you'll find you won't need to reach for a paper or calculator at all.
Be sure to check out the Rounding 2 video
to learn how to round off to the nearest hundred and thousand.
In the meantime, you can keep practicing rounding with our fun online games and quizzes.
And, remember to always be clever.