Transcript Percent of a Number

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Objective
Find the percent of a number
Vocabulary
None
Example 1 Use a Proportion to Find a Percent
Example 2 Use Multiplication to Find a Percent
Example 3 Use Multiplication to Find a Percent
SURVEYS Out of 1,423 adults surveyed, 30% said they
knew the name of their mail carrier. How many of the
people surveyed knew their mail carrier’s name?
Write a ratio of those that knew the
name to the total adults surveyed
Define the variable
Number that knew name = x
Total number in survey is denominator
number that knew name →
total number in survey →
1/3
SURVEYS Out of 1,423 adults surveyed, 30% said they
knew the name of their mail carrier. How many of the
people surveyed knew their mail carrier’s name?
Remember: 30% refers to 30 out of 100
Write the percent in ratio form
Put an = sign between the 2 ratios to
make a proportion
number that knew name →
total number in survey →
1/3
SURVEYS Out of 1,423 adults surveyed, 30% said they
knew the name of their mail carrier. How many of the
people surveyed knew their mail carrier’s name?
Find the cross product
Multiply
100  x = 1,423(30)
100x = 42,690
Ask “What is being done to
the variable?”
The variable is being
multiplied by 100
Do the inverse on both
sides of the equal sign
1/3
SURVEYS Out of 1,423 adults surveyed, 30% said they
knew the name of their mail carrier. How many of the
people surveyed knew their mail carrier’s name?
Bring down 100x = 42,690
100  x = 1,423(30)
100x = 42,690
Using the fraction bar,
divide both sides by 100
Combine “like” terms
Since cannot have part of a
person, round to the nearest
whole number
Add dimensional analysis
x = 426.9
Answer: x = 427 people knew carriers name
1/3
SURVEYS Out of 765 students surveyed, 42% said that
they watch some television after school before doing their
homework. How many of the students surveyed watch
some television after school before doing their homework?
Answer: 321 students watch TV after school
before doing homework
1/3
What number is 120% of 24?
x = 1.2  24
x = 28.8
Translate English to algebra
Change 120% to a decimal
The variable is by itself so
multiply
Answer: x = 28.8
2/3
What number is 160% of 44?
Answer: x = 70.4
2/3
Find 25% of $600.
x = 0.25  600
x = 150
Translate English to algebra
Change 25% to a decimal
The variable is by itself so
multiply
Answer: x = $150
3/3
*
Find 80% of $450.
Answer: x = $360
3/3
Assignment
Lesson 7:7
Percent of a Number
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