SOLUTION: My problem is with entering e raised to a negative power on my TI-84 Plus calculator. I know what answer I need to get and I can't figure out how to enter the problem correctly.

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Question 191254: My problem is with entering e raised to a negative power on my TI-84 Plus calculator. I know what answer I need to get and I can't figure out how to enter the problem correctly. I've looked on line and through my calculator manual to no avail!
The problem is: If 18 g of a radioactive substance are present initially and 3 yr later only 6 g remain, how much of the substance will be present after 11 yrs?
I get to the equation y=18e ^-.2310 x 7 and I know my answer is 5.02 grams, but how do I do this on my calc to get this answer? Thanks for any help!
Answer by Edwin McCravy(20056)   (Show Source): You can put this solution on YOUR website!
 


When , , plug those in:







Substitute 18 for P in



When , , plug those in:





Divide both sides by 18




Use principle  is equivalent to 



Divide both sides by 3



In your TI-84 type  ln(1/3)/3 ENTER and get -.3662040962



Substitute -.3662040962 for r in



 

Now we substitute 11 for t

 





So after 11 years, there are only .3205 grams.

Edwin
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