Question 1208600
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Bismuth-210 is an isotope that radioactively decays by about 13% each day, meaning 13% of the remaining Bismuth-210 
transforms into another atom (polonium-210 in this case) each day. If you begin with 215 mg of Bismuth-210, how much remains after 7 days?
After 7 days, mg of Bismouth-210 remains.
Round your answer to the nearest hundredth as needed.
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The remaining mass of the Bismuth-210 after 1 day is  215*(1-0.13) = 215*0.87 mg.


The remaining mass of the Bismuth-210 after 2 days is  215*0.87*0.87 = 215*0.87^2 mg.


The remaining mass of the Bismuth-210 after 3 days is  215*0.87^2*0.87 = 215*0.87^3 mg.


. . . . . and so on . . . . . 


The remaining mass of the Bismuth-210 after 7 days is  215*0.87^6*0.87 = 215*0.87^7  = 81.10978 mg  (rounded).    <U>ANSWER</U>
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Solved, with explanations.