document.write( "Question 1102943: A scientist begins with 100 milligrams of a radioactive substance that decays exponentially. After 38 hours, 50 mg of the substance remains. How many milligrams will remain after 54 hours? (Round your answer to two decimal places.) \n" ); document.write( "

Algebra.Com's Answer #717650 by greenestamps(13216) $\"\"$ $\"About$

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\n" ); document.write( "The solution by the other tutor is valid. However, with rounding error, the answer you will get with her solution (37.29mg) will NOT be correct to 2 decimal places. If you use her method, you need to keep more decimal places in your intermediate calculations in order to get an answer that is correct to 2 decimal places.

\n" ); document.write( "But her method is also a LOT more work than is necessary to get the answer; there is a MUCH easier and more straightforward way.

\n" ); document.write( "The given information tells you immediately that the half life of the substance is 38 hours.
\n" ); document.write( "The given time of 54 hours is 54/38 half lives.
\n" ); document.write( "So the amount remaining after 54 hours, rounded to 2 decimal places, is
\n" ); document.write( " $\"100%2A%281%2F2%29%5E%2854%2F38%29+=+37.34\"$ \n" ); document.write( "

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