document.write( "Question 529827: A tank contains 20 gallons of antifreeze solution. When it is full, it contains 15% antifreeze. How many gallons must be replaced by an 80% antifreeze solution to get 20 gallons of a 70% solution? \n" ); document.write( "
Algebra.Com's Answer #349771 by ankor@dixie-net.com(22740)\"\" \"About 
You can put this solution on YOUR website!
A tank contains 20 gallons of antifreeze solution.
\n" ); document.write( " When it is full, it contains 15% antifreeze.
\n" ); document.write( "How many gallons must be replaced by an 80% antifreeze solution to get 20 gallons of a 70% solution?
\n" ); document.write( ":
\n" ); document.write( "Let x = amt of 15% solution removed, and the amt of 80% solution to be added
\n" ); document.write( ":
\n" ); document.write( ".15(20-x) + .80x = .70(20)
\n" ); document.write( "3 - .15x + .80x = 14
\n" ); document.write( "-.15x + .80x = 14 - 3
\n" ); document.write( ".65x = 11
\n" ); document.write( "x = \"11%2F.65\"
\n" ); document.write( "x = 16.9 gal removed and 16.9 gal of 80% antifreeze to be added
\n" ); document.write( ":
\n" ); document.write( ":
\n" ); document.write( "Check this: 20-16.9 = 3.1 gal of 15% solution remains
\n" ); document.write( ".15(3.1) + .8(16.9) = 14
\n" ); document.write( ".465 + 13.52 = 13.985 ~ 14 \n" ); document.write( "
\n" );