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January 31st, 2014, 11:16 PM  #1 
Newbie Joined: Dec 2013 From: Seattle, WA Posts: 14 Thanks: 0  Help with exponential functions
The problem: "Suppose you deposit $2000 in a savings account that pays interest at an annual rate of 4%. How many years will it take for the account to contain $2500?" So I created the equation, which is y = 2000(1.04)^x My question is, how do I solve this without guessing and checking on my calculator? How do I solve this algebraically? I think I do this: 2500 = 2000(1.04)^x I'm sure I'm incorrect, like always, but what's the next step? PEMDAS? 
February 1st, 2014, 12:33 AM  #2 
Senior Member Joined: Jun 2013 From: London, England Posts: 1,316 Thanks: 116  Re: Help with exponential functions
You need to use the natural logarithm: 
February 1st, 2014, 12:43 AM  #3  
Newbie Joined: Dec 2013 From: Seattle, WA Posts: 14 Thanks: 0  Re: Help with exponential functions Quote:
 
February 1st, 2014, 03:34 AM  #4  
Global Moderator Joined: Dec 2006 Posts: 21,035 Thanks: 2271  Quote:
It is possible that the interest is not added to the account, but instead paid to the account holder, in which case the account will never contain $2500.  
February 1st, 2014, 04:05 AM  #5  
Math Team Joined: Sep 2007 Posts: 2,409 Thanks: 6  Re: Help with exponential functions Quote:
The wording "that pays interest at an annual rate of 4%" makes me think it is simple interest. Quote:
 

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