document.write( "Question 330573: if the cost for materials to make a circular metal disk 3 cm in diameter is $.15, what would be the cost for materials to make a disk of the same thickness but 6 cm in diameter?
\n" ); document.write( "would the answer be $.45? Thanks. \n" ); document.write( "

Algebra.Com's Answer #236996 by Fombitz(32388) $\"\"$ $\"About$

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The assumption is that the cost of materials is based on the area of the disk (since the thickness is equivalent).
\n" ); document.write( " $\"T=C%2AA\"$ , where $\"T\"$ is total cost, $\"C\"$ is cost per unit area, $\"A\"$ is area.
\n" ); document.write( "The area of a circle is,
\n" ); document.write( " $\"A1=%28pi%2F4%29%2AD%5E2=%28pi%2F4%29%2A3%5E2=%289%2F4%29%2Api\"$
\n" ); document.write( "From the first example,
\n" ); document.write( " $\"0.15=C%2A%289%2F4%29%2Api\"$
\n" ); document.write( " $\"C=0.15%2F%28%289%2F4%29%2Api%29\"$
\n" ); document.write( "The area for the second disk is,
\n" ); document.write( " $\"A2=%28pi%2F4%29%2A6%5E2=9pi\"$
\n" ); document.write( "Since A2 is 4 times as much as A1, then the total cost will be 4 times as much.
\n" ); document.write( " $\"T=%28%280.15%29%2F%28%289%2F4%29%2Api%29%29%2A%289%2Api%29=%280.15%29%284%29=0.60\"$
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\n" ); document.write( "$0.60 \n" ); document.write( "

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