S
ECTION
3.3 P
ART
2
P
ERCENTAGE
OF
A
N
UMBER
:
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Suppose there’s an old teacher in your school but you
don’t know exactly how old he is.
IF you are told that 50% of his age is 32. How old is
this teacher?
So we know that:
At the same time:
So this means that
Mr. Old is 64 years old.
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In this section, you will be given percentage of an
unknown number and then asked to find the value of
that unknown number
Ex: 30% of an unknown number is 15. What is the
unknown number?
Suppose we have a box and the area is equal to the value
of this unknown number
Now, 30% of the area is equal to 15
Before we find the area of the whole
shape, find the area of one tiny box:
So the area of one tiny box is 0.5 units
Since there are 100 tiny boxes, the
area of the entire shape is:
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Practice: 24% of a number is 15.72. What is the unknown
number?
Practice: James has some money in his wallet. Edward
has $30 and is 40% of James amount. How much does
James have?
First find the area of one tiny
box, which is the value of 1%
So 1% is equal to 0.655
Then find the area of the entire
box, which is the value of 100%
1% of James money is:
So 1% of James money
is 75 cents
Then find the value of all the James
money in his wallet:
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Ex: Brian and his girlfriend went to a fancy restaurant for
dinner. After he paid, he forgot how much the dinner
was. The only thing he remember was that he gave a 15%
tip of $8.25. How much did the dinner cost?
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Homework:
Handout 3.3 part 2
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I
MAGE
:
http://stockfresh.com/image/1008216/old-teacher
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