**Intro to Chemistry and Physics Index**

**Where are we going with this?**Rounding off numbers in math is very important to accurately communicate science information

**Rounding Numbers (is easy)**

(Round numbers? Like zero, six, nine, and eight? Is 3 a round number or a crooked number? And what about two?)

The idea of rounding numbers is to express a long decimal number more concisely. For this discussion, the whole principle of significant figures is going to be passed over. We are going to just be looking at the rounding process.

### Step 1

Figure out how many decimal places you need. This could be dictated by directions in a problem or proper use of significant figures.

__In the examples that follow you will be rounding to ONE decimal place.__

### Step 2

Look at your number. Find the decimal place. Count over to the digit you are going to round.

Perhaps, as you develop skills, you should underline that number.

EXAMPLE: 123

*4*.__7__ABxyzVITAL TO UNDERSTAND!!!!

The only things that can change are:

1. The digit to which you are rounding (underlined above).

2. The digit that comes before it (italics above).There is a 95% chance you will NOT change this.

### Step 3

Look at your digit that comes after the one you are rounding off. In the example it's the green A.

EXAMPLE: 123

*4*.__7__ABxyz### Step 4

### If the A is less than 5:

Chop off the A and everything after it. Done.

1234.7ABxyz

becomes

1234.7

If the A is greater than 5:

Increase the number you are rounding by 1 and chop off the rest. Done.

1234.7ABxyz

becomes

1234.8

__Notice that we don't care what the B is!__

SPECIAL CASE:

When the number in the place we are rounding is a 9

EXAMPLE: 123*4*.__9__ABxyz

__Notice that we don't care what the B is!__

When the number in the place we are rounding is a 9

*4*.

__9__ABxyz

### If the A is less than 5:

Chop off the A and everything after it. Done.

1234.9ABxyz

becomes

1234.9

If the A is greater than 5:

Increase the number you are rounding by 1 (makes it a 10, write a 0), then increase the number before the one you are rounding by 1. Then chop off the rest. Done.

## 123

4.9ABxyz

becomes

1235.0

__Notice that we don't care what the B is!__

__Notice that we don't care what the B is!__