Question 81859: a certain isotope has a half life of three hours. if you start w/7945 grams, how many grams will there be 2 days from now?
Found 2 solutions by kev82, Nate:
Answer by kev82(151)   (Show Source):
You can put this solution on YOUR website! Hi,
You may have been given an exponential decay equation you are supposed to work with, but as you haven't posted it. I'll show you how to solve the problem without it.
Every 3 hours, the amount of the isotope halves. So, if you start with  of it. Then after 3 hours you will have  of it. Then after another three hours you will have half left again, so you will have  of it left. So the question basicaly boils down to, "how many times will it halve in 2 days?", or more clearly "how many 3 hours are there in 2 days?"
Well, that's easy to work out, 2 days is 48 hours, and 48/3=16. So the amount will halve 16 times in 2 days. The original amount was 7945 grams, so the amount you'll have left is:
According to my calculator that is approximately 0.121 grams
Hope that helps,
Kev
Answer by Nate(3500) (Show Source):
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