SOLUTION: If a bank returns $25,000 with compounded interest, how long was the money left in the bank? rate of 8%. How do I use logarithms to find the answer? I have tried to use my textbook

Algebra ->  Logarithm Solvers, Trainers and Word Problems -> SOLUTION: If a bank returns $25,000 with compounded interest, how long was the money left in the bank? rate of 8%. How do I use logarithms to find the answer? I have tried to use my textbook      Log On


   

Question 29185: If a bank returns $25,000 with compounded interest, how long was the money left in the bank? rate of 8%. How do I use logarithms to find the answer? I have tried to use my textbook for help but I still do not understand. Thank you.
Answer by atif.muhammad(135) About Me  (Show Source):
You can put this solution on YOUR website!
This question cannot be solved without knowing how much money there was originally in the bank.
x * %281.08%29%5Ey = 25000
where x = amount of money at the start, y=number of years the money was there.
x= 20000 (according to your reply!)
20000 * %281.08%29%5Ey = 25000
%281.08%29%5Ey = 25000%2F20000
%281.08%29%5Ey = 1.25
This calls for us to use the 3rd Logarithmic Law.
If you need to know which one I'm talking about, then consult this website:
http://www.themathpage.com/aPreCalc/logarithms.htm#laws

%281.08%29%5Ey = 1.25
y%2A+log+%281.08%29 =+log+1.25
y = %28log+1.25%29+%2F+%28log+1.08%29
y = 2.899435195 years
We will round off the number of years to the nearest whole number. However, your textbook may not so use my answer below with caution.
y = 3yrs. The money was there for 3 years.