What am I doing wrong: Volume of a cylinder

[pooky2]

Can someone please tell me what I'm doing wrong?

I get 2 different answers for the volume of a cylinder that has radius 12 inches and length 40 feet depending on if I convert to ft or inches first. And yes I'm converting back with the answers... still comes out different.

Radius - 12" Length 40'

 

[tkhunny]

One must convert units correctly.

[math]\pi r^{2}h = \pi (1 ft)^{2} (40 ft) = 40\pi ft^{3}[/math] = 125.6637061435916 ft^3

[math]\pi r^{2}h = \pi (12\; in)^{2} (40*12 \;in) = 69120\pi\;in^{3}[/math] = 217146.8842161262848 in^3

Are they the same?

217146.8842161262848 / 12 / 12 / 12 = 125.6637061435916

With enough decimal places, it looks like we have it.

 

[pooky2]

There it is. I knew I was just missing some simple step somewhere... I was only dividing my final answer by 12 once... duh Thank you SO much!!!!

 

[tkhunny]

There it is. I knew I was just missing some simple step somewhere... I was only dividing my final answer by 12 once... duh Thank you SO much!!!!

That was my guess. That's why I figured I would just demonstrate it. Off you go, then...