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Lecture 7

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MU123

Discovering Mathematics

Week 7

Discovering Finance

Discovering Finance
Dr. Hassan Sharafuddin
Week 7 Learning Outcomes

This unit includes the following sections:


- Solving for different values using the simple
interest formula. (30 minutes)
- Calculating Present value (30 minutes)
- Solving Quiz 2 (30 minutes)

- Discuss solutions (20 minutes)

Discovering Finance
Dr. Hassan Sharafuddin
The Simple Interest Formula

Interest is money. And if you’re the borrower, you pay for


the privilege of using the money. If you’re the lender,
you’re paid the interest for your service of providing the
money.

The amount of money being borrowed or loaned is the


principal, or the initial amount. The rate of interest is
the percentage of the principal that it costs to borrow the
money (or that you’re paid for using the money). And the
time is the period — in years, months, or days —that the
transaction is taking place.

Discovering Finance
Dr. Hassan Sharafuddin
Find simple interest using
the simple interest formula
The Simple Interest Formula

I=PxRxT

Discovering Finance
Dr. Hassan Sharafuddin
HOW TO: Identify the principal, rate and time
The Simple Interest Formula

 The price paid for using money is called interest.


 Principal is the amount borrowed or invested.
 Rate is the percent of the principal paid as
interest per period, usually one year.
 Time must be expressed in the same unit
of time as the rate. (i.e. one year)

Discovering Finance
Dr. Hassan Sharafuddin
The Simple Interest Formula

The interest formula shows how interest, principal, rate,


and time are related and gives us a way of finding one
of these values if the other three values are known.
Interest = principal * rate * time
I =P *R *T
I = PRT
If the rate is a percent per year, the time must be
expressed in years or a decimal or fractional part of a
year.
Similarly, if the rate is a percent per month, the time
must be expressed in months.

Discovering Finance
Dr. Hassan Sharafuddin
Key Terms…
The Simple Interest Formula

 Interest
– An amount paid or earned for the use of money.
 Simple interest
– Interest earned when a loan or investment is
repaid in a lump sum.
 Principal
– The amount of money borrowed or invested.

MORE

Discovering Finance
Dr. Hassan Sharafuddin
Key Terms…
The Simple Interest Formula

 Rate
– The percent of the principal paid as interest
per time period.
 Time
– The number of days, months or years that the
money is borrowed or invested.

Discovering Finance
Dr. Hassan Sharafuddin
HOW TO: Find the interest paid on a loan
The Simple Interest Formula

Principal = (P) = $1,200


Interest rate = 8% (or 0.08)
Time = 1 year
Interest = P x R x T
Interest = 1,200 x 0.08 x 1
Interest = $96
The interest on the loan is $96

Discovering Finance
Dr. Hassan Sharafuddin
The Simple Interest Formula

Simple interest is frequently used when small businesses act


as lenders in order to sell products and arrange for payments
over the next two years rather than at the end of the time
period. For example:

Amal purchases a new car from a local dealer. She makes


arrangements with the dealer to pay for the $23,995 car over
the next 4 years at 5% interest (simple interest). If she is to
make equal monthly payments, how much are those
payments?

Discovering Finance
Dr. Hassan Sharafuddin
The Simple Interest Formula

Discovering Finance
Dr. Hassan Sharafuddin
Find the Principal, Rate or Time
Using the Simple Interest Formula

The I=PRT formula allows you to solve for more than just
the amount of interest accumulated. You also can use the
formula to find the value of any of the variables — if you
have the other three.
For instance, you can determine the interest rate from the
amount of interest paid. Example:

Shafi agreed to make quarterly payments of $781.25 for 4


years on a loan of $10,000. What simple interest rate is he
paying?

Discovering Finance
Dr. Hassan Sharafuddin
Find the Principal, Rate or Time
Using the Simple Interest Formula

You first need to determine the total amount of money being


repaid. If Shafi is making 4 payments a year for 4 years, you
know that he’s making 16 payments of $781.25.
So his total repayment is 16 × $781.25 = $12,500.
You also know that he borrowed $10,000, so the interest he’s
paying is: $12,500 –$10,000 = $2,500.
The interest amount, $2,500, is the answer to the interest
formula, I = PRT.
So replace the I with $2,500, replace P with $10,000, replace
T with 4, and then solve for R.

Discovering Finance
Dr. Hassan Sharafuddin
Find the Principal, Rate or Time
Using the Simple Interest Formula

Discovering Finance
Dr. Hassan Sharafuddin
Examples…
Section 11-1 The Simple Interest Formula

 Find the interest on a 2-year loan of $4,000 at a


6% rate.
– $480
 Find the interest earned on a 3-year investment of
$5,000 at 4.5% interest.
– $675

Discovering Finance
Dr. Hassan Sharafuddin
Home Assignment

Discovering Finance
Dr. Hassan Sharafuddin
Find the maturity value of a loan
The Simple Interest Formula

 Maturity value is the total amount of money


due by the end of a loan period.
– The amount of the loan and interest.
 If principal and interest are known, add them.
– MV = principal + PRT
– MV = P(1+RT)

Discovering Finance
Dr. Hassan Sharafuddin
An Example…
The Simple Interest Formula

Marcus Logan can purchase furniture on a 2-year


simple interest loan at 9% interest per year.
What is the maturity value for a $2,500 loan?
MV = P(1 + RT); (substitute known values)
MV = $2,500 (1 + 0.09 x 2)
MV = $2,500 (1 + 0.18)
MV = $2,500 (1.18)
MV = $2,950
Marcus will pay $2,950 at
the end of two years.
Discovering Finance
Dr. Hassan Sharafuddin
Examples…
The Simple Interest Formula

 Amjad is going to borrow $4,000 at 7.5%


interest. What is the maturity value of the loan
after three years?
– $4,900
 Hanan will invest $3,000 at 8% for 5 years.
What is the maturity value of the investment?
– $4,200

Discovering Finance
Dr. Hassan Sharafuddin
Calculating Present Value

The simple interest method is restricted primarily to


loans and investments having terms of less than one
year.

The compound interest method is employed in cases


where the term exceeds one year.

In the compound interest method, interest is periodically


calculated and converted to principle. It means that
interest is added to the principle and is thereafter treated
as principal.

Discovering Finance
Dr. Hassan Sharafuddin
Calculating Present Value

Example:
Susan secured a small business loan of $8000 for three
years, compounded annually. If the interest rate was 9%, find
the future value (compound amount).
Solution:
There are three interest periods, one for each of the three
years.
First year = 8000 + (8000 x 0.09 X 1)
= 8000 + 720 = 8720 (this is maturity for year 1)
Second year = 8720 + (8720 X 0.09 X 1)
= 8720 + 784.8 = 9504.8 (MV for year 2)
Third year = 9504.8 + 9504 X 0.09 X 1)
= 9504.8 + 855.43 = 10360.23 (MV for year 3)
The future value is $10,360.23
Discovering Finance
Dr. Hassan Sharafuddin
Calculating Present Value

Discovering Finance
Dr. Hassan Sharafuddin
Calculating Present Value

Exercise:
 A loan of $2,950 at 8% is made for two years
compounded annually. Find the future value
(compound amount) of the loan. Find the amount
of interest paid on the loan.
 Answer:
The future value = $3,440.88
The compound interest = $490.88

Discovering Finance
Dr. Hassan Sharafuddin
Calculating Present Value

Discovering Finance
Dr. Hassan Sharafuddin
Calculating Present Value

Exercise:
Compute the amount of money to be set aside today
to ensure a future value of $2,500 in one year if the
interest rate is 2.5% annually, compounded annually.
Answer:
$2439.02 (to 2 d.p.)

Discovering Finance
Dr. Hassan Sharafuddin
Solve Quiz 2 (30 minutes)
Discuss solutions (20 minutes)

Discovering Finance
Dr. Hassan Sharafuddin

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