SOLUTION: Suppose that 5 grams of a radioactive substance decreases to 4 grams in 30 seconds. What is its half-life to the nearest tenth of a second?

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Question 324617: Suppose that 5 grams of a radioactive substance decreases to 4 grams in 30 seconds. What is its half-life to the nearest tenth of a second?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
N=N0e%5E%28kt%29
+4=5e%5E%28k%2830%29%29
e%5E%2830k%29=4%2F5
30k=ln%284%2F5%29
k=ln%284%2F5%29%2F30
k=-0.007438
.
.
.
e%5E%28kt%29=1%2F2
kt=ln%281%2F2%29
t=ln%281%2F2%29%2F%28-0.007438%29
t=93.2
The half life is 93.2 seconds.