Transcript Wonderful world of Decimals

WONDERFUL WORLD
OF DECIMALS 
What is a
decimal
number?
A decimal
is a part of
a whole.
• Think about money
1 dollar and 4 dimes
•1.40$
Whole
Part of the
whole
On a number line
1
4
0
Converting from fraction to Decimal
• THERE ARE 2 WAYS
• 1) You can write the fraction with a denominator that is a
power of 10.
• (10,100,1000….)
Denominator is the bottom number of a fraction
• Ex
•
𝟑
𝟓
𝒙𝟐
𝒙𝟐
=
𝟔
𝟏𝟎
Step 2
• Than move your decimal place one spot to the
left, because the 10 has 1 zero.
•
6.
0 .6
More examples
245
•
1000
How many decimal points will I move to
the left?
245.
Look at money again.
• It takes 10 dimes to make 1
dollar.
So 1 dime is 1 tenth
1
10
of the whole
It takes 100 pennies to make 1 dollar
A penny is one hundredth of
1
a dollar
100
Second way
• Divide the numerator by the
denominator.
7
•
16
•7÷16
•=0.4375
Express the following mixed fraction as a
decimal
•
2
2
3
=2. a decimal
•2÷3 =0.66
•2.66
Homework
• Pg 90#15,16,17
• Pg 91# 18,19,20
Comparing decimal numbers
• If 2 decimal numbers have different wholes
• Ex.
• 4.56
and
7.89
• The one with the larger whole is bigger.
Comparing decimal numbers
• If the 2 numbers have the same whole but different
decimal numbers.
• 6.54
and
6.43
• The one with the larger tenth digit is bigger
Adding and subtracting decimals
• Example :
235.7 +18.276
• 1) Write digits with the same position under each other
and line up the decimal point.
•
235.7
•
+ 18.276
• 2) Add or (subtract) the numbers ignoring the decimal
point.
•
•
235.7
+ 18.276
Adding and subtracting decimals
• 3) Place the decimal point directly under the decimal of
the other numbers.
•
•
•
•
2 3 5 .7
+ 1 8 .2 7 6
2 5 3. 976
Homework
Pg 94#1-5
Word Problem
• You are going shopping for groceries and you want to
save as much money as possible. Here are the prices at 2
stores:
Item
Loblaws
Super C
Milk
3.59$ a litre
3.55$ a litre
Bread
4.39$
3.99$
Eggs
5.19$ for 12
4.39 $ for 12
Yogart
2.99$ for 2
3.45$ for 6
Which Grocery store would give you the best
deal overall and how much would it cost?
Pg 95
• #7-11
Multiplication and division of decimals
• 1) When multiplying by a power of ten (10,100,1000…)
Move the decimal one place to the right for every zero
Example: 3.45 X100
3.45
=345.00
Multplication with decimal numbers
Move the decimal one place to the Left for every
zero.
003.45 =.00345
Multiplication
• For all other numbers,
• 1) Multiply them as if they were not decimal numbers.
•
•
•
•
•
•
•
•
35.18
X 4.7
24 626
+ 1 40 720
1 65 346
2) Count the number of decimal places in the 2 numbers
we have 3.
3) Put the decimal place in the result so it is same as the
total of the 2 numbers.
Homework
• Pg 96
• ALL
• Pg 97 #3 & 4