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 or subtract as usual.
Ex.
2.4 + 3.1
2.4
+ 3.1
5.1
6.78 - .345
6.780 (put in the 0 placeholder)
- .345
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) multiply as if they were whole numbers
3) count the number of digits to the right of the decimal point in each number – get the total
4) 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)
x 3.5 (1 digit after decimal point)
2060
12300
14.360 (3 digits after decimal point)
total of 3 digits after decimal point
DIVIDING DECIMALS
To divide decimals:
1) set up like a regular long division problem
2) if the divisor (# on the outside) is a decimal, move the decimal point to the right until it is a whole
number (if the divisor is a whole number, just divide as usual)
3) move the decimal point in the dividend (the # inside) the same number of spaces to the right as you
moved it in the divisor
4) bring the decimal point up into the quotient (so you won’t forget it)
5) divide as usual
ex.
8.31 ÷ 4.2
4.2 8.31
1.978 (round to 1.98)
42 83.100
- 42
411
- 378
330
-294
360
336
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