SOLUTION: Radium-221 has a half-life of 30s. How long will it take for 95% of a sample to decay?

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Question 81510This question is from textbook Precalculus
: Radium-221 has a half-life of 30s. How long will it take for 95% of a sample to decay? This question is from textbook Precalculus

Answer by Nate(3500) About Me  (Show Source):
You can put this solution on YOUR website!
There would be 0.05a left if the initial amount was a after x years.
0.05a = a(0.5)^x
0.05 = (0.5)^x
log(0.05) = x * log(0.5)
log(0.05) / log(0.5) = x
x = about 4.32
4.32... * 30 = 129.65784 years