I am in school and trying to work through this example in the book. It all works out except the Theoretical Flow Rate which the book specifies as 15.3 GPM. From a little research I believe the issue is with how MathCad defines rpm but I can not figure it out. 
Any help would be greatly appreciated,
Frank
Don't divide by 231 - Mathcad knows units so it's going to do that on it's own, you're forcing it to do it twice.
Also, you have a unit of revolution in your input but none in your output. So, Mathcad is going to divide by 2*pi to get rid of it. Dealing with anything rpm related can be tricky.
So without the 231 and 2*pi factors you get the expected answer.
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