Do you recognize this formula?

This happens to be the formula for simple interest, where*I* = simple interest, *P* = principal, *R* = annual percentage rate, and *T* = time
in years.

This happens to be the formula for simple interest, where

**In this problem we need to solve for T.
This means we need to get T on one side
and
EVERYTHING ELSE on the other side using inverse operations.**

Let’s solve this formula for T:

***Formula solved for T**

3

Let’s solve this formula for* y*:

***Inverse of mult. by -7 is div.
by -7**

***Formula solved for y**

***Divide num. by -7**

***Another way to write it**

A principle of $50,000 is invested into a CD paying an annual percentage rate of 7.5%. Find the amount in the account after 10 years if the account is compounded monthly.

Make sure that you read the question carefully several
times.

Since we are looking for compound interest, we will need
the **compound
interest formula: **

The variables in this formula represent the following:

*A* = end amount in the
account

*P* = principal (starting
amount)

*r* = annual rate of interest

*t *= time in years

*n* = number of times
compounded per year

In this problem,

A = ? = this is the variable we are looking for

*P *= 50000

*r *= 7.5% = .075

*t *= 10

*n* = 12 (There are
12 months
in a year)

A = ? = this is the variable we are looking for

**Plugging the values into the formula we get:**

***Add inside the ( )**

***Raise 1.00625 to the exponent of
120**

***Multiply**

If you take $50000 and compound it monthly for 10 years, you do end up with 105603.23

**FINAL ANSWER: ** **The compound amount is $105603.23.**

In Nebraska on I-80, the speed limit is 75 mph. How long would it take you to travel 525 miles in Nebraska on I-80 if you went the speed limit the whole time?

Make sure that you read the question carefully several
times.

Since we are looking for how long it would take you to travel, we can use the distance/rate formula:

*d *= *rt*

The variables in this formula represent the following:

*d *= distance

*r *= rate

*t *= time

In this problem,

*d *= 525

*r *= 75

*t *= = ? = this is the
variable we are looking
for

*d *= *rt*

**Plugging the values into the formula we get:**

If you go at a rate of 75 miles per hour for 7 hours, you would travel 525 miles.

**FINAL ANSWER: ** **It would take 7 hours.**

Sally is training for the Olympics. She likes to run around a circular track that has a diameter of 60 yards, 20 times during a workout. How many yards does she run during her workout?

Make sure that you read the question carefully several
times.

Since we are needing to find the circumference of a circle, we can use this formula:

The variables in this formula represent the following:

*C* = circumference of a
circle

*r *= radius

In this problem,

*C *= ? = this is the variable
we are looking
for

*r = *30 (radius is half
of the diameter,
so r = 60/2 = 30)

**Plugging the values into the formula we get:**

First, find the circumference of a circle.

***Replace pi with 3.14 for an approximate
value**

For every workout, she runs around the track 20
times. So, we
need to multiply the circumference by 20 to find the number of yards
that
she runs during her workout.

***Multiply using approx. value
**

If you take 2 times 30 you do get 60, so the circumference checks out. If you take 20 times 60 you do get 1200, so the number of yards ran in a workout checks out.

**FINAL ANSWER: ** **The number of yards that she runs in a workout
is ****1200 or approximately
3768.**

Last revised on July 3, 2011 by Kim Seward.

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