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```							Adding and Subtracting
Decimals
NS11

1
 Recall that when we add or subtract
money, we write the numbers so that the
decimal points are vertically aligned.
 This way we are sure to add digits with the
same place value.
 We insert the decimal point in the answer
below the other decimal points, as shown
above.

2
 We use the same procedure to add or
subtract any decimal numbers.
 We keep the decimal points in line.
 This way, we add or subtract digits with
the same place value.
 The decimal points stay in a straight line,
as shown above.

3
Let’s practice!
   Find the perimeter of the
triangle. Units are in
centimeters.
   How do we find perimeter?
   We keep the decimal points
aligned in the problem so we
can add digits with the same
place value.
   We add the digits column by
column, just as we would add
whole numbers or money.

4
Another Example:
   The roof was 6.37 meters above
reach only 4.2 meters. The roof
was how much higher than the
   We line up the decimal points
vertically so that we subtract
digits with the same place value.
   We attach a zero to 4.2 so that
there are no empty places in the
problem. Then we subtract.
5
   To add digits with the same place
value, we align decimal points.
   In this problem the whole number 3
has the same place value as the 6
and the 4.
   We place a decimal point to the
right of the 3 and align decimal
points.
   We may fill empty decimal places
with zeros if we wish.

6
   For some subtraction
problems we need to
perform the
subtraction.
   If we subtract 0.23
from 0.4, we find
there is an “empty”
place in the problem.
   We fill the empty
place with a zero.
Then we subtract.

7
Subtract: 0.4 – 0.231
   We set up the
problem by lining up
the decimal points,
remembering to write
the first number on
top.
   We fill empty places
with zeros.
   Then we subtract.

8
Subtract: 3 – 1.23
   This problem is
similar to subtracting
\$1.23 from \$3.
   We place the decimal
point to the right of
the 3, fill the decimal
places with zeros,
and subtract.

9
4.3 + 2
a.   4.5
b.   6.3
c.   4.1
d.   2.3

10
4 + 1.3 + 0.6
a. 2.3
b. 5.3
c. 5.9
11
4.75 – 2
a. 2.75
b. 4.73
c. 6.75
d. 4.77
12
0.3 – 0.15
a. 0.25
b. 0.15
c. 0.12
d. 0.18
13
1 – 0.1
a. 0.9
b. 1.1
c. 0

14
2.5 – 1
a. 2.4
b. 2.6
c. 1.6
d. 1.4
15
1 – 0.25
a. 0.24
b. 0.75
c. 1.25
d. 0.15
16
The end!
17

```
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