document.write( "Question 174611This question is from textbook Algebra and Trigonometry Structure and Method Book 2
\n" ); document.write( ": I'm not sure on how to start the following:
\n" ); document.write( "When mineral deposits formed a coating 1mm thick on the inside of a pipe, the area through which the fluid can flow was reduced by 20%. Find the original inside diameter of the pipe.
\n" ); document.write( "It also gives me the equations for area of a circle and diameter.
\n" ); document.write( "Help is appreciated.
\n" ); document.write( "Thank you. \n" ); document.write( "
Algebra.Com's Answer #129632 by checkley77(12844)\"\" \"About 
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The formula for the area of a circle is pir^2
\n" ); document.write( "Thus:
\n" ); document.write( ".8pir^2=pi(r-1)^2
\n" ); document.write( ".8*3.14r^2=3.14(r^2-2r+1)
\n" ); document.write( "2.514r^2=3.14r^2-6.28r+3.14
\n" ); document.write( "3.14r^2-2.514r^2-6.28r+3.14=0
\n" ); document.write( ".626r^2-6.28r+3.14=0
\n" ); document.write( "Using the quadratic equation we get 9.504 mm. for the original inside radius of the pipe.
\n" ); document.write( "Proof:
\n" ); document.write( ".8*3.14*9.504^2=3.14*(9.504-1)^2
\n" ); document.write( "2.512*90.326=3.14*8.504^2
\n" ); document.write( "226.9=3.14*72.318
\n" ); document.write( "227~227 \n" ); document.write( "
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