# Is my book answer incorrect?

• Apr 26th 2009, 09:43 AM
garms
Hi,

I have a simple Volume problem that I would like some assistance with please: I have a Cylinder of Duct work measuring 6' long and 6" (diameter) or height. I need the Volume of aire inside it so I am using the following formula: \$\displaystyle V = pi r^2 h\$
\$\displaystyle V = (3.141592)(3in)^2 (72in)\$
\$\displaystyle V = (3.141592)(9in)(72in)\$
\$\displaystyle V = (3.141592)(648)\$
\$\displaystyle V = 2035.75"^2\$

Now my book has an answer of \$\displaystyle 1.2^3\$ feet.

What in the world am I doing wrong? (Thinking)

I am so confused here. If only the book would give more than just an answer...

TIA,
GA
• Apr 26th 2009, 10:17 AM
masters
Quote:

Originally Posted by garms
Hi,

I have a simple Volume problem that I would like some assistance with please: I have a Cylinder of Duct work measuring 6' long and 6" (diameter) or height. I need the Volume of aire inside it so I am using the following formula: \$\displaystyle V = pi r^2 h\$
\$\displaystyle V = (3.141592)(3in)^2 (72in)\$
\$\displaystyle V = (3.141592)(9in)(72in)\$
\$\displaystyle V = (3.141592)(648)\$
\$\displaystyle V = 2035.75"^2\$

Now my book has an answer of \$\displaystyle 1.2^3\$ feet.

What in the world am I doing wrong? (Thinking)

I am so confused here. If only the book would give more than just an answer...

TIA,
GA

Hi garms,

You converted your units to inches, so the result came out in inches cubed.

To covert back to feet cubed, you will need to divide by 12 cubed (1728) because that's how many cubic inches there are in 1 cubic foot.