document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1207769>Question 1207769</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A 39-ounce can of Hills Bros.® coffee requires 188.5 square inches of aluminum. If its height is 7 inches, what is its radius? \r<BR>\n" );
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document.write( "[Hint: The surface area S of a right cylinder is S = 2(pi)(r^2) + 2(pi)rh, where r is the radius and h is the height.\r<BR>\n" );
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document.write( "I say the set up I'd this:\r<BR>\n" );
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document.write( "188.5 = 2(pi)(r^2) + 2(pi)7r\r<BR>\n" );
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document.write( "I now must find r.\r<BR>\n" );
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document.write( "Yes?  </SPAN>\n" );
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document.write( "S = 2pi*r^2 + 2pi*r*h<BR>\n" );
document.write( "S = 2pi*r(r + h)<BR>\n" );
document.write( "188.5 = 2pi*r(r + 7)<BR>\n" );
document.write( "r(r+7) = 188.5/(2pi)<BR>\n" );
document.write( "r(r+7) = 30.00070677 approximately\r<BR>\n" );
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document.write( "I used my calculator's stored version of pi to get the most accuracy possible when computing the right hand side.<BR>\n" );
document.write( "If we rounded to say 1 decimal place, then that 30.00070677 becomes 30.0 or simply 30.<BR>\n" );
document.write( "I'm rounding to one decimal place because 188.5 is to the same level of accuracy.<BR>\n" );
document.write( "Please let me know if your teacher wants some other level of accuracy instead.\r<BR>\n" );
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document.write( "r(r+7) = 30<BR>\n" );
document.write( "r^2+7r = 30<BR>\n" );
document.write( "r^2+7r-30 = 0<BR>\n" );
document.write( "(r+10)(r-3) = 0<BR>\n" );
document.write( "r+10 = 0 or r-3 = 0<BR>\n" );
document.write( "r = -10 or r = 3<BR>\n" );
document.write( "A negative radius is not possible. We'll ignore it.<BR>\n" );
document.write( "The only practical solution is r = 3.\r<BR>\n" );
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document.write( "Let's check this radius.<BR>\n" );
document.write( "S = 2pi*r^2 + 2pi*r*h<BR>\n" );
document.write( "S = 2pi*r(r + h)<BR>\n" );
document.write( "S = 2pi*3(3+7)<BR>\n" );
document.write( "S = 60pi<BR>\n" );
document.write( "S = 188.49555922 approximately when using a calculator<BR>\n" );
document.write( "S = 188.5 when rounding to one decimal place.<BR>\n" );
document.write( "This confirms we have the correct radius value when considering the rounding method mentioned.\r<BR>\n" );
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document.write( "Answer: 3 inches<BR>\n" );
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