SOLUTION: Question Help After the release of radioactive material into the atmosphere from a nuclear power plant in a country in 1990​, the hay in that country was contaminated by a rad

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Question 1140194: Question Help
After the release of radioactive material into the atmosphere from a nuclear power plant in a country in 1990​, the hay in that country was contaminated by a radioactive isotope​ (half-life 5 ​days). If it is safe to feed the hay to cows when
15​% of the radioactive isotope​ remains, how long did the farmers need to wait to use this​ hay?
__ days
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
x = 0 for year 1990

y=pe%5E%28-kx%29
-
1%2F2=e%5E%28-k%2A5%29
ln%281%2F2%29=-5k
k=ln%282%29%2F5
-
y=pe%5E%28-.1386x%29

----
If it is safe to feed the hay to cows when
15​% of the radioactive isotope​ remains, how long did the farmers need to wait to use this​ hay?
----

Solve for x with
0.15=e%5E%28-0.1386x%29
.
.