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Lesson Menu
Five-Minute Check (over Lesson 76) Then/Now New
Vocabulary Example 1 Find Simple
Interest Example 2 Real-World Example Find the
Interest Rate Example 3 Find the Total
Amount
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5-Minute Check 1
Find the percent of change from 15 to 18. Is
the change a percent of increase or a percent of
decrease?
A. 3 increase B. 10 increase C. 20
increase D. 22 increase
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5-Minute Check 2
Find the percent of change from 80 lb to 72 lb.
Is the change a percent of increase or a percent
of decrease?
A. 8 decrease B. 10 decrease C. 15
decrease D. 20 decrease
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5-Minute Check 3
Find the percent of change from 325 ft to 280 ft.
Is the change a percent of increase or a percent
of decrease?
A. 13.8 decrease B. 13.6 decrease C. 13.4
decrease D. 13.2 decrease
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5-Minute Check 4
Myra bought a new car. Her monthly car payment
went from 294 to 324. Find the percent of
change.
A. 10.7 increase B. 10.6 increase C. 10.5
increase D. 10.2 increase
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5-Minute Check 5
Which of the following has a percent of decrease
of 18?
A. from 475 to 389.5 B. from 150 to 177 C. from
625 to 112.5 D. from 315 to 371.7
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Then/Now
You have already solved problems using the
percent equation. (Lesson 75)

• Solve simple interest problems and apply the
  simple interest equation to real-world problems.

• Solve compound interest problems.

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Vocabulary

• interest

• simple interest
• principal
• compound interest

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Example 1A
Find Simple Interest
A. Find the simple interest for 2000 invested at
2.5 for 3 years.
I prt Write the simple interest
formula. I 2000 ? 0.025 ? 3 Replace p with
2000, r with 0.025, and t with 3. I 150
Simplify.
Answer The simple interest is 150.
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Example 1B
Find Simple Interest
B. Find the simple interest for 4500 invested at
4.25 for 2 years.
I prt Write the simple interest
formula. I 4500 ? 0.0425 ? 2 Replace p
with 4500, r with 0.0425, and t with 2. I
382.50 Simplify.
Answer The simple interest is 382.50.
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Example 1A
A. What is the simple interest for 3000 invested
at 3.5 for 2 years?
A. 105 B. 150 C. 210 D. 350
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Example 1B
B. What is the simple interest for 2500 invested
at 2.75 for 4 years?
A. 137.50 B. 275 C. 302.75 D. 412.50
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Example 2
Find the Interest Rate
SWIMMING POOL Mr. Webster borrowed 1280 to buy
a new swimming pool. He will pay 57.60 each
month for the next 24 months. Find the simple
interest rate for his loan.
Understand You need to find the simple
interest rate. Plan Use the formula I
prt. Solve First, find the amount of interest he
will pay over 24 months. 24 ? 57.60
1382.40 Multiply to find the total amount.
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Example 2
Find the Interest Rate
1382.40 1280 102.40 Subtract to find
the interest.
The principal is 1280. So, p 1280. The loan
will be for 24 months or 2 years, so t 2.
I prt Write the simple interest
formula. 102.40 1280 ? r ? 2 Replace I with
102.40, p with 1280, and t with
2. 102.40 2560r Simplify.
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Example 2
Find the Interest Rate
Divide each side by 2560.
0.04 r
Answer The simple interest rate is 0.04 or 4.
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Example 2
Mrs. Wymer borrowed 5100 to remodel her kitchen.
She will pay 238 a month each month for the next
24 months. What is the simple interest rate for
the loan?
A. 4.5 B. 5 C. 5.5 D. 6
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Example 3
Find the Total Amount
What is the total amount of money in an account
where 800 is invested at an interest rate of
6.25 compounded annually for 2 years?
Step 1 Find the amount of money in the account at
the end of the first year.
I prt Write the simple interest
formula. I 800 ? 0.0625 ? 1 Replace p with
800, r with 0.0625, and t with 1. I
50 Simplify.
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Example 3
Find the Total Amount
800 50 850 Add the amount invested and
the interest.
At the end of the first year, there is 850 in
the account.
Step 2 Find the amount of money in the account
at the end of the second year.
I prt Write the simple interest
formula. I 850 ? 0.0625 ? 1 Replace p with
850, r with 0.0625, and t with 1.
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Example 3
Find the Total Amount
I 53.13 Simplify.
Answer So, the amount in the account after 2
years is 850 53.13 or 903.13.
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Example 3
What is the total amount of money in an account
where 1000 is invested at an interest rate of
3.5 compounded annually for 2 years?
A. 1035.00 B. 1070.00 C. 1071.23 D. 1092.41
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End of the Lesson