Rounding Decimals

Intro to Algebra

Why round?

On your calculator, take 132 ÷ 789

The answer is .16730038

Why round?

But we don’t want to write all that.

Most of it is so small that it doesn’t even have an effect on the number.

We round the answer to make it shorter, but still very close to the actual answer!

Note

When we round, we make our answer less accurate, but it is easier to use.

How to round

In this class, when there is a need to round, I will tell you what to round to.

Examples:• Round your answer to the nearest whole

number• Round your answer to the nearest hundredth

How to round

The first step in rounding is to locate the place value that you are rounding.

Example:Round 8.546 to the nearest tenth.

Which number is in the tenths place?

How to round

We will keep everything in front of the place value, and we will determine what to put in the tenths place.

Example:Round 8.546 to the nearest tenth.

Keep 8.__

How to round

To determine which number to put in the blank, we will look at the number after the place value we are rounding to.

Example:Round 8.546 to the nearest tenth.

Which number is after the tenths place?

How to round

Then we will follow these two rules:1. If the following number is 0, 1, 2, 3, or 4 – Keep the

number that is currently in the position we are rounding (round down)

2. If the following number is 5, 6, 7, 8, 9 – We add 1 to the number that is currently in the position we are rounding (round up)

Example:Round 8.546 to the nearest tenth.

Round up or down?

Let’s put it all together!

1. Find the place value we are rounding2. Keep everything in front of that place value3. Look at the number after that place value to

determine whether we round up or down1, 2, 3, or 4 – Round Down5, 6, 7, 8, or 9 – Round Up

Let’s try some examples!

Note

These rules do not always apply to rounding in real life examples, but they will in this class.

Can you think of any examples where we wouldn’t follow these rounding rules?