Decimal Subtraction (3 or more decimal places)

The process of subtracting numbers with decimals is exactly the same as the process of subtracting whole numbers.  The only difference is in the set-up.

And, no matter how many decimal places you have, it's the same process. With longer numbers, just be careful to line up decimals and fill in empty place values with zeros so you don't forget to borrow!

No matter what size numbers you're working with, if even one number has a decimal, you have to line the numbers up by their decimal points.  

$$\require{cancel}\eqalign{3457&\\-12&.68762\\\hline\text{ }}$$

And, because in subtraction, it's so easy to forget to borrow, we recommend putting decimals after whole numbers and filling in empy place values with zeros so that both numbers in the subtraction problem extend the same number of places to the right. 

$$\eqalign{3457&.00000\\-12&.68762\\\hline \text{}}$$

Those extra zeros may seem a little silly, but once they are there students are much less tempted to make the most common decimal subtraction error: forgetting to borrow (without a zero on top, it's just so easy to bring that bottom number down!):

$$\eqalign{3\,4\,5\overset{6}{\cancel{7}}\!&.\overset{9}{\cancel{0}}\!\overset{9}{\cancel{0}}\!\overset{9}{\cancel{0}}\!\overset{9}{\cancel{0}}\!^1\!0\\-1\,2&.\,\,6\,\,8\,\,7\,\,6\,\,2\\\hline3\,4\,4\,4&.\,\,3\,\,1\,\,2\,\,3\,\,8}$$

So, basically, when subtracting decimals: take your numbers, line them up vertically by the decimal  (add the decimal to the end of whole numbers), fill in zeros so that the numbers extend the same distance to the right, and then subtract normally!