Question 1147320
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Solve {{{.5^x = .12}}} to find the number of half-lives it takes for the percentage to reach 12%; then multiply by the number of days in the half life to find the number of days.<br>
The half life of 6 days is presumably an approximate number; and radioactive decay is random and not "smooth". So an approximation for an answer should be sufficient; using exactly 6 days for the half life and exactly 12% for the remaining percentage to get an answer to 5 or 6 decimal places is unrealistic.<br>
Since .5^3 = .125 = 12.5%, the remaining percentage will be very close to 12% after 3 half lives, which is 3*6 = 18 days.