DECIMAL RULES

ADDING & SUBTRACTING DECIMALS

To add or subtract decimals:
1)	line up the decimal points (this will automatically line up your place values)
2)	add zeros as placeholders as needed 
3)   estimate the sum or difference
4)   add or subtract as usual.

Ex.	2.4  + 3.1	2.4	6.78 - .345	6.780 (put in the 0 placeholder)
 + 3.1	   -  .345
5.1	6.435

MULTIPLYING DECIMALS

To multiply decimals:
1)	line up last digit in each number (just like you would if you were multiplying whole numbers – put
number with most digits on top)
2)	 Estimate the product 
3)	multiply as if they were whole numbers
4)	count the number of digits to the right of the decimal point in each number – get the total
5)	make sure your answer has the same number of digits (total) to the right of the decimal point

ex.	3.5 x 4.12	4.12  (2 digits after decimal point)	total of 3 digits after decimal point
 x 3.5  (1 digit after decimal point)
2060
 12300
14.360 (3 digits after decimal point)

DIVIDING DECIMALS

To divide decimals:
1)  set up as a regular long division problem
 2)  if the divisor is a decimal, move the decimal point to the right until it is a whole
number	(multiplying by powers of 10 moves decimal point) 
3)  move the decimal point in the dividend the same number of spaces to the right as you
moved it in the divisor    (multiplying by powers of 10 moves decimal point)
4)  bring the decimal point up into the quotient (so you won’t forget it)
5)  divide as usual
6) add decimal place to dividend and add place holder zeros if need to get to thousandths place 

1.978  (round to 1.98)
ex.	8.31 ÷ 4.2	4.2  8.31	42   83.100
- 42
411
- 378
330
  -294
360
 336
24