An element with mass 210 grams decays by 8.3% per minute. How much of the element is remaining after 15 minutes, to the nearest 10th of a gram?

Answer 1

If the element decays at 8.3% per minute, that means after each minute another 8.3% is gone. The percentage that remains is 100% - 8.3% which is 91.7%, After 0 minutes there is 210 grams, After 1 minute the amount that remains is 210(0.917). After another minute the amount that remains is [210(0.917)] (0.917).

This an exponential decay function:

y = 210(0.917)^t

To determine amount left after 10 minutes find y(10), i.e. substitute 10 for t.

y(10) = 210(0.917)¹⁰

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