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After the release of radioactive material into the atmosphere from a nuclear power plant in a country in 2000, the hay in that country was contaminated by a radioactive
isotope (half-life 7 days). If it is safe to feed the hay to cows when 14% of the radioactive isotope remains, how long did the farmers need to wait to use this hay?
The farmers needed to wait approximately days for it to be safe to feed the hay to the cows.
(Round to one decimal place as needed.)
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sqdancefan

Answer:

  19.9 days

Step-by-step explanation:

The amount remaining after d days is ...

  a = (1/2)^(d/7)

We want to find d when a = 0.14

  log(a) = (d/7)log(1/2)

  d = 7·log(0.14)/log(1/2) ≈ 19.855 ≈ 19.9

The farmers need to wait about 19.9 days for it to be safe.

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