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: 1234.7ABxyz
VITAL 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: 1234.7ABxyz
Step 4
If the A is less than 5:
Chop off the A and everything after it. Done.
1234.7ABxyzbecomes
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: 1234.9ABxyz
When the number in the place we are rounding is a 9
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.
1234.9ABxyz
becomes
1235.0
Notice that we don't care what the B is!
Notice that we don't care what the B is!