Download VUB Mini Course Beginning Signed Numbers Addition & Subtraction ... ADDITION OF SIGNED NUMBERS

VUB Mini Course Beginning Signed Numbers Addition & Subtraction
Name________
ADDITION OF SIGNED NUMBERS
1. If the signs are the same ADD the two numbers. Keep the sign.
2. If the signs are different SUBTRACT the two numbers. The answer takes the sign of
the larger of the two numbers.
SUBTRACTION OF SIGNED NUMBERS
If the signs are different SUBTRACT the two numbers. The answer takes the sign of the
larger number.
Let’s look at the following problems including some with decimals and fractions.
There will be more notes and problems with fractions and decimals to follow.
Perform indicated operation. Use pencil and show all work neatly. Reduce fractions.
 11   3  14
This is an add problem.
The signs on both numbers are
negative. We add the two numbers
and the final answer is negative.
1.
 10  15  10   15  25
This is a subtract problem. Change the
subtract sign to an add sign and change
the following sign to its opposite. Then
follow the rule for adding signed
numbers.
 10  15  25
Many students will not show any work
on this type of problem. They write the
answer directly.
 30  23   7
5.
This is an add problem. The signs are
different. So we subtract the two
numbers. The final answer takes the
sign of the larger number so it is
negative.
3.
 12   8   12   8  4
This is a subtract problem. Change the
subtract sign to an add sign and change the
following sign to its opposite. Then follow the
rule for adding signed numbers.
2.
It is customary to write the + (+8) just as 8.
 12   8   12   8   4
2  9  7
4.
This is an add problem. The signs are
different. So we subtract the two numbers.
The final answer takes the sign of the larger
number so it is positive.
 65  50   15
This is an add problem. The signs are
different. So we subtract the two numbers.
The final answer takes the sign of the larger
number so it is negative.
6.
 20   9   20  9   11
This is a subtract problem. Change the
subtract sign to an add sign and change
the following sign to its opposite. Then
follow the rule for adding signed
numbers.
17   3  17  3  20
This is a subtract problem. Change the
subtract sign to an add sign and change the
following sign to its opposite. Then follow the
rule for adding signed numbers.
7.
8.
9.
 3.6  2.6   6.2
This is a subtract problem with
decimals. Change the subtract sign to
an add sign and change the following
sign to its opposite. Then follow the rule
for adding signed numbers.
10.
We must line up the decimals when
adding or subtracting decimals. Many
students will not show any work if they
can do the work mentally. They write
the answer directly.
 3 .6
We must line up the decimals when adding
or subtracting decimals. It was necessary to
add a zero to make the numbers have the
same number of decimal places. We
subtract the two numbers and the answer is
negative.
 8.30
 2 .6
 8.3  6.15   2.15
This is an add problem. The signs are
different. So we subtract the two numbers.
The final answer takes the sign of the larger
number so it is negative.
 6.15
 6.2
 2.15
11.

3
1
9
4
13

 

 
4
3
12
12
12
This is a subtract problem with fractions.
Therefore we must write the fractions as
equivalent fractions with the same
denominator. The least common
denominator is 12, so change each
denominator to 12. Each numerator will
then change. Multiply each numerator
by the same number that each
denominator was multiplied by.
Once we have like fractions add or
subtract the numerators as needed and
keep the denominator the same.
The final answer will be negative.
12.
4
4
6
28 30
58
 6
   
 


5
5
7
35 35
35
 7
This is a subtract problem with fractions.
Therefore we must write the fractions as
equivalent fraction with the same
denominator. The least common
denominator is 35, so change each
denominator to 35. Each numerator will then
change. Multiply each numerator by the
same number that each denominator was
multiplied by.
Once we have like fractions add or subtract
the numerators as needed and keep the
denominators the same.
The final answer will be positive.
13.

3
2
9 16
7




8
3
24 24 24
This is an add problem with fractions.
Therefore we must write the fractions as
equivalent fractions with the same
denominator. The least common
denominator is 24, so change each
denominator to 24. Each numerator will
then change. Multiply each numerator
by the same number that each
denominator was multiplied by.
Once we have like fractions add or
subtract the numerators as needed and
keep the denominator the same.
The final answer will be positive.
14.
5
4 35
24
11




6
7 42
42
42
This is a subtract problem with fractions.
Therefore we must write the fractions as
equivalent fractions with the same
denominator. The least common
denominator is 42, so change each
denominator to 42. Each numerator will then
change. Multiply each numerator by the
same number that each denominator was
multiplied by.
Once we have like fractions add or subtract
the numerators as needed and keep the
denominator the same.
The final answer will be positive.