DECIMAL NUMBERS
10 of 0.1 is adding of 10 0.1s = 1
0.1
+ 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 +0.1 + 0.1 = 1.0
10
tenths = 1 one
DECIMAL NUMBERS: ADDITION
Example
Add 7.3 and 14.5
Method
Step1: Line numbers using the decimal point
7.3
+14.52
Step2:
7.30
+14.52
Step3: Add
7.30
+14.52
21.82
Why Is It Okay To Fill The Decimal Number With Zero
The zero is to
show that there is no value at that decimal place.
12.5
is the same as 12.50 or 12.500
Example
Add 237 and 8.42 and 25.8
Method
Step1: Line
the number using the decimal point
237
8.42
+25.8
Step2: ‘Fill’ zero to equal decimal place
237.00
8.42
+25.80
Step3: Add
237.00
8.42
+25.80
271.22
ESTIMATE TO CHECK IF THE ANSWER IS REASONABLE
Example
Add 6.3 and 12.6
Method
Step1: Line
the number using the decimal point
6.3
+12.8
Step2: ‘Fill’ zero to equal decimal place
6.3
+12.8
Step3: Add
6.3
+12.8
19.1
ESTIMATE:
Step1: Round off
each number
6.3 = 6, 12.8 = 13.
Step2: Add the
numbers
6 + 13 = 19
Step3: Compare the
number.
The difference is 0.1. The answer is
reasonable.
DECIMALS: SUBTRACTION
Example
Subtract 1.5 from 8.73
Method
Step1: Line
the number using the decimal point
8.73
-1.5
Step2: ‘Fill’ zero to equal decimal place
8.73
-1.50
Step3: Subtract
8.73
-1.50
7.23
Word Problems
Example (1)
Dave and Sally have
a total mass of 82.15 kg. Sally’s mass is 39.6. What is Dave’s mass?
Step1:
Underline keywords and list objects
Sally Dave
Step2: Draw Model
Step3: Solve
Step1:
Align Decimal point
82.15
- 39.60
Step2:
‘Fill’ zero to equal decimal place
82.15
- 39.60
Step3:
Subtract
82.15
-39.60
43.55
Dave’s mass is 43.55
kg
Example (2)
Amy jogged a
distance of 2.6km and walked a distance of 1.25 km. What was the total distance
that Amy covered?
Step1: Underline keywords and list objects
Amy
Step2: Draw Model and link numbers
Step3: Solve
Step1:
Align Decimal point
2.6
+ 1.25
Step2:
‘Fill’ zero to equal decimal place
2.60
+ 1.25
Step3:
Subtract
2.60
+ 1.25
3.85
km
Amy covered a
distance of 3.85 km
