This document discusses adding and subtracting decimals. It explains that when adding or subtracting decimals, the decimal points must be vertically aligned so that digits of the same place value are added or subtracted. Empty spaces can be filled in with zeros. Several examples of adding and subtracting decimals are provided and worked through step-by-step.

1. 1
Adding and Subtracting
Decimals
NS11

2. RECALL -Place Value
1,0001,000 100100 1010 11 0.10.1 0.010.01 0.000.00
11
0.0000.000
11

3. 3
 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.

4. 4
 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.

5. 5
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.

6. 6
Another Example:
 The roof was 6.37 meters above
the ground. The ladder could
reach only 4.2 meters. The roof
was how much higher than the
ladder could reach?
 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.

7. 7
Add: 6.2+3+ 4.25
 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.

8. 8
 For some subtraction
problems we need to
add decimal places 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.

9. 9
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.

10. 10
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.

11. 11
a. 4.5
b. 6.3
c. 4.1
d. 2.3
4.3 + 2

12. 12
4 + 1.3 + 0.6
a.2.3
b.5.3
c.5.9

13. 13
4.75 – 2
a. 2.75
b. 4.73
c. 6.75
d. 4.77

14. 14
0.3 – 0.15
a. 0.25
b. 0.15
c. 0.12
d. 0.18

15. 15
1 – 0.1
a. 0.9
b. 1.1
c. 0

16. 16
2.5 – 1
a. 2.4
b. 2.6
c. 1.6
d. 1.4

17. 17
1 – 0.25
a. 0.24
b. 0.75
c. 1.25
d. 0.15

18. 18
The end!