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
Look at money again.
• It takes 10 dimes to make 1
dollar.
So 1 dime is 1 tenth
1
10
or 0.1
of the whole
It takes 100 pennies to make 1 dollar
A penny is one hundredth of
1
a dollar
or 0.01
100
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
Multiplication of decimals
• 1) When multiplying by a power of ten (10,100,1000…)
Move the digit one place to the LEFT for every zero
Example: 3.45 X100
3.45
=345.00
Multiplication with decimal numbers
Move the digit one place to the RIGHT 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.
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?