document.write( "Question 122467: A solution has a concentration of 10 milligrams of salt per cubic centimetre. Water is slowly added such that the concentration of salt is reduced by 20% every two hours. Determine the equation that models the concentration of salt in terms of time and use it to find the concentration after 7 hours. \n" ); document.write( "

Algebra.Com's Answer #89992 by ankor@dixie-net.com(22740) $\"\"$ $\"About$

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A solution has a concentration of 10 milligrams of salt per cubic centimetre. Water is slowly added such that the concentration of salt is reduced by 20% every two hours. Determine the equation that models the concentration of salt in terms of time and use it to find the concentration after 7 hours.
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\n" ); document.write( "Let t = time in hours
\n" ); document.write( "Let A = resulting amt
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\n" ); document.write( "A 20% reduction leaves 80% changed to decimal .8
\n" ); document.write( "Use the exponent t/2 because it's every two hours
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\n" ); document.write( "A = 10 * .8^(t/2)
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\n" ); document.write( "In 7 hrs:
\n" ); document.write( "A = 10 * .8^(7/2)
\n" ); document.write( "A = 10 * .4579; (find .8^3.5 on a calc)
\n" ); document.write( "A = 4.579 milligrams after 7 hrs \n" ); document.write( "

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