SOLUTION: Hand sanitizer kills a certain bacterium 80% of the time on each application. What is the minimum number of times you must use the hand sanitizer to be 98% certain you have killed

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Question 762773: Hand sanitizer kills a certain bacterium 80% of the time on each application. What is the minimum number of times you must use the hand sanitizer to be 98% certain you have killed that bacterium?
Answer by tommyt3rd(5050) About Me  (Show Source):
You can put this solution on YOUR website!
We'll write:
P=0.8%5En
and 98% implies P=1-0.98 = 0.02

Solving...
ln%28P%29=ln%280.8%5En%29

n=ln%280.02%29%2Fln%280.8%29=17.53

so we need to apply 18 times

:)