Learning Objectives for Section 3.1Simple Interest
After this lecture, you should be able to
Compute simple interest using the simple interest formula.
Solve problems involving investments and the simple interestformula.
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Some Preliminary Notes
Financial institutions often use 360 days for one year when computingtime.
Time must be in terms of years to use in the formulas.
All rates (%) must be converted to decimals to use in formulas.
When an answer is rounded, use the symbol instead of =.
We will round to the nearest cent for dollar amounts, unless otherwisestated.
Try to avoid rounding until the final answer.
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Conversions: Time Periods
Example 1: Convert the given time periods into years:
a)180 daysb) 120 daysc) 3 quarters
d) 7 monthse) 60 daysf) 26 weeks
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Conversions: Percents to Decimals
Example 2: Convert the given percents to decimals:
a)4.5%b) .32%c) 112%
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Conversions: Decimals to Percents
Example 3: Convert the given decimals to percents:
a) 0.06b) 5c) 0.11
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Simple Interest Formula
Simple Interest Formula
where
I = interest
P = principal (amount invested or amount of loan)
r = annual simple interest rate (as a decimal)
t = time in years
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An Example
Example 4: Find the interest on a boatloan of $5,000 at 16% for 8 months.
Example 5: What is the total amount to be paid back onthe boat loan in Example 4?
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Total Amount to Be Paid Back
In general, the future value (amount) is given by the followingequation:
A = Principal + Interest
A = P + I
A = P + Prt
A = P (1 + rt)
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Another Example
Example 6: Find the total amount due on a loan of $600 at 16%
interest at the end of 15 months.
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Another Example
Example 7:A loan of $10,000 was repaid at the end of 6 months.
What amount (principal and interest) was repaid, if a 6.5% annual
rate of interest was charged?
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Application
Example 8: A department store charges 18.6% interest (annual)for overdue accounts. How much interest will be owed on a$1,080 account that is 3 months overdue?
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Interest Rate Earned on a Note
Example 9: What is the annual interestrate earned by a 33-day T-bill with amaturity value of $1,000 that sells for$996.16?
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Purchase Price of a Note
Example 10:What is the purchase price of a 26-week T-billwith a maturity value of $1,000 that earns an annual interestrate of 4.903%?