Decimal Addition
The
first time your students are faced with decimal numbers might be a bit shocking
to them, but actually there’s not much difference between operations with decimals
and operations with whole numbers. Generally speaking, these operations need to
be done more carefully –if they are not, the students’ results might differ
greatly from the correct answer. You can find exercises and drills to help your
students practice the content of this lesson at the Decimals page
of our website
In
this article, we want to deal with the most basic operation of all, that is,
decimal addition. First of all, let’s see a very simple sum:
As
you can see, decimal addition is performed exactly as integer addition, except
for the placement of the decimal comma in the result. The comma’s position is
probably the most important thing to consider when dealing with decimal
addition. Each addend’s comma must be aligned with the rest (see image):
Notice
that the addends’ digits are also aligned around the decimal comma. This remains
true even when the number before the comma is a zero:
A
“trick” that could help to align the digits, is to fill the empty spaces with zeros,
until both numbers are the same length before and after the decimal:
In
this case, we must remember that except for the first zero before the decimal,
none of these zeroes is normally written, and serve only as a “crutch” until
the student is able to work without them.
Until
now we have only seen sums with no regrouping. The principle is the same behind
integer addition with regrouping, while also considering the placement of the
decimal. So, 6.6 + 5.5 becomes:
If
both addends are between zero and one, we operate in the same way:
It’s
the same even when we add a number greater than one, with a number between zero
and one:
These
are the basics of decimal addition. Obviously, the student must have a good
understanding of integer addition beforehand, since decimal addition is an extension
of it. Once the student notices the relationship between them, and learns the
details of decimal addition, s/he should have no problems, as they apply to any
number, regardless of how many digits it has:
We
hope you find this lesson useful. You can find more articles, drills and free
math goodies at our site, Math-Drills.com.
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