Pre Algebra Decimal Number Manipulation
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Point Two
Decimal Number Manipulation

 
 A dollar just happens to be cut into 100 slices. 
 What if it wasn't? 
 
 There is nothing so special about a number 
 with 2 places on the right side of the decimal point.
 If our a dollar was cut up into 1000 pieces, 
 we would need 3 number places 
 (called decimal places in fancy math talk) 
 on the right side:
 

 $1.000

 
 We could still add this stuff up the same way. 
 Just remember that the decimal point on all numbers MUST line up:
 
 Examples:
 
 Add .391 and .608 ...
 

 
 Subtract .206 from .978 ...
 

 
 In fact, we could have any number of places 

 on the right of the decimal point:

 
 Examples:
 

 
 What happens if we have 2 numbers to add that look like this:
 

 .3157  +  .23

 
 First, we line up the decimal points:
 

 
 WAIT A MINUTE! 
  There are 4 digits in the first number and only 2 in the second one!
 
 So?
 
 Don't all the numbers have to have the same number of places 
 on the right side of the decimal point?
 
 NO! They do not!
 If it makes you feel better, you can put in zeros after the .23 
 until it has as many digits as the other number. 
 The zeros won't change the value at all.
 
 Now lets add:
 

 
 Subtraction works the same way:
 
 Example:
 

 .83 - .011

 
 Step 1:
 

 
 Step 2:
 

 

 
 Step 3:
 

 
 OK, Now look at this one ...
 
 Example:
 

 
 How do we deal with this puppy?
 
 Remember the elevator? 
 This time, each floor is .1 instead of 1.
 

 
 Did you notice that the decimal didn't really change the steps at all?
 

 

 

   copyright 2005 Bruce Kirkpatrick

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