Question 1050239
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How many feet of piping can be made from 5 cubic feet of iron if the outer diameter of the pipe is 16 inches and the inner diameter is 12 inches? 
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Your guiding equation is

5 = {{{pi*8^2*L - pi*6^2*L}}}.   (1)

{{{pi*8^2*L}}} is the volume of the cylinder of the radius 8 = {{{16/2}}} inches and the length of L feet.

{{{pi*6^2*L}}} is the volume of the cylinder of the radius 6 = {{{12/2}}} inches and the length of L feet.

The difference is the volume of the pipe, which is a hollow cylinder.

The number "5" in the left side of the equation (1) is the given volume of the iron.

Simplify (1):

5 = {{{pi*L*(64-36)}}} = {{{pi*L*28}}},

hence

L = {{{5/(28*pi)}}}.

Use your calculator.
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