Adding and subtracting with decimals is easy IF you think of decimals as MONEY. Why? Well, everyone has had some experience with buying stuff and you have to know something about money if you're going to go shopping! That little-bitty decimal point is going to be really important if it is in the WRONG place when you're spending your allowance or babysitting money…think about it. If the sales clerk tells you your bill is $1000.00 instead of $100.00, you'd definitely want to be certain that the amount is correct!
Step 1: Line up the Decimal Points
When you add or subtract decimals, you must ALWAYS remember to LINE UP the decimal points.
Lining up the decimal points in a VERTICAL (up-and-down) manner will make things super-duper easy (and if you have graph paper, even better because you can write each numeral in its own square).
Let's say you have the following:
8.256 + 321.4
Write the first addend (i.e., the first number you are adding) then write the make a decimal point under the first one. Begin writing the second addend, carefully writing the numbers in their correct places…
Step 2: Do the math
Add a zero as a place-holder for any spot that doesn't have a number.