How many cubic yards of concrete are needed to build a concrete pipe 9 feet long and 9 inches thick if the interior diameter must be 54 inches? (round tot eh nearest hundredth)

Question

campbell_st · Answer

if the interior diameter is 54 inches then the interior radius is 27 inches. 

the exterior radius will be 27 + 9 = 36 inches

you need to find the area between the 2 circles... 

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but before calculating convert all your measurements to yards... since you need to find the volume in cubic yards. 


27 inches = 0.75 yards

36 inches = 1 yard

9 ft = 3 yards


find the area between the circles  

Area = Big Circle - Little Circle

$$A = \pi \times 1^2 - \pi \times 0.75^2 $$

when you know the area, to find the volume multiply by the length of the pipe


$$V = A \times 3$$

You will need to round your answer to 2 decimal places... 

hope this helps.

anonymous · Answer

THANKS!