document.write( "Question 194023: The fish population of a lake is modeled by the function \r
\n" ); document.write( "\n" ); document.write( "P=(10)/(1+4e^(-0.8t))\r
\n" ); document.write( "\n" ); document.write( "where, P is the number of fish in thousands and t is the years since the lake was stocked.\r
\n" ); document.write( "\n" ); document.write( "What is the fish population (correct up to two decimal places) after 3 years is? [Remember: If P=3.15, then there are 3,150 fish)\r
\n" ); document.write( "\n" ); document.write( "How many years will it take for the fish population to reach 7,000? (correct up to two decimal places)
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Algebra.Com's Answer #145647 by josmiceli(19441)\"\" \"About 
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P is the number of fish in thousands
\n" ); document.write( "(a)
\n" ); document.write( "\"t+=+3\"
\n" ); document.write( "\"P=10+%2F+%281+%2B+4e%5E%28-.8t%29%29\"
\n" ); document.write( "\"P=10+%2F+%281+%2B+4e%5E%28-2.4%29%29\"
\n" ); document.write( "\"P=10+%2F+%281+%2B+4%2A.0907%29\"
\n" ); document.write( "\"P=10+%2F+%281+%2B+.3629%29\"
\n" ); document.write( "\"P=10+%2F+%281.3629%29\"
\n" ); document.write( "\"P+=+7.34\"
\n" ); document.write( "the population is 7,340 after 3 years
\n" ); document.write( "(b)
\n" ); document.write( "\"P+=+7\"
\n" ); document.write( "\"P=10+%2F+%281%2B4e%5E%28-.8t%29%29\"
\n" ); document.write( "\"7=10+%2F+%281%2B4e%5E%28-.8t%29%29\"
\n" ); document.write( "Multiply both sides by \"%281%2B4e%5E%28-.8t%29%29\"
\n" ); document.write( "\"7%2A%281%2B4e%5E%28-.8t%29%29+=+10\"
\n" ); document.write( "\"1+%2B+4e%5E%28-.8t%29+=+10%2F7\"
\n" ); document.write( "\"4e%5E%28-.8t%29+=+3%2F7\"
\n" ); document.write( "\"e%5E%28-.8t%29+=+3%2F28\"
\n" ); document.write( "Take the ln of both sides
\n" ); document.write( "\"-.8t+=+ln%28.10714%29\"
\n" ); document.write( "\"-.8t+=+-2.2336\"
\n" ); document.write( "\"t+=+2.79\" years
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