SOLUTION: A scientist begins with 100 milligrams of a radioactive substance that decays exponentially via the function f(x)=a×b^x. After 2 hours, 70 milligrams of the substance remains. 1.

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Question 1148464: A scientist begins with 100 milligrams of a radioactive substance that decays exponentially via the function f(x)=a×b^x. After 2 hours, 70 milligrams of the substance remains.
1. Find a?
2. Find b?
4. How many milligrams will remain after 13 hours?

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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A scientist begins with 100 milligrams of a radioactive substance that decays exponentially via the function f(x)=a×b^x.
After 2 hours, 70 milligrams of the substance remains.
1. Find a?
a = initial amt, 100 mg
:
2. Find b?
x = 2 hrs, f(x) = 70
100%2Ab%5E2+=+70
b^2 = 70%2F100
b = sqrt%28.7%29
b = .867
4. How many milligrams will remain after 13 hours?
f%28x%29+=+100+%2A+.867%5E13
f(x) = 15.64 mg after 13 hrs