Question 1113664
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The cost C of steel tubing is jointly proportional to its length L​, in​ feet, and diameter D​, in inches.
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{{{C=k*LD}}}


{{{k=C/(LD)}}}


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If a 2 foot tube with a 3 inch diameter costs ​$12​,...
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{{{k=12/(2*3)}}}


{{{k=2}}}


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{{{highlight_green(C=2*LD)}}}