A stuffed animal dealer tells you that a fish he bought for $8 four years ago is now worth $200 follow the steps below to find the effective yield for this investment.

Begin with the equation 8(1+r) ^4=200.Solve for (1+r) ^4
Take the common logarithm of each side of the equation.

Use the power property of Logarithms to rewrite log (1+r) ^4
Solve the equation for log (1+r)
Use exponential logarithmic inverse property to eliminate the logarithm
(Hint: Remember that these are common logarithms) Then solve for R.

If the current trend continues, how much will a $1000 investment in stuffed fish be worth in 3 years?

and how long will it be until you can buy a $1800 computer

3 answers

8(1+r)^4=200 , divide both sides by 8
(1+r)^4=25
take the fourth root of both sides, no logs needed
1 + r = 25^(1/4) = 2.23606...
r = 1.2306..
the effective rate is appr 123%

so after 3 years, a $1000 investment will be worth
1000(1 + 1.2306067..)^3
= 1000(2.2306067..)^3
= .....

for the last part:
1800 = 1000(2.2306067..)^t
you will need logs for this one
What do you do for the last part
From the instructions to the question, I was assuming
you are studying logarithms
You MUST be able to do a simple equation like this:
1800 = 1000(2.2306067..)^t
hint: divide both sides by 1000, then take log of both sides.
I assume you have a scientific calculator.