yogi_Compute GPA For Number Of Tests Taken Ignoring N/A For Tests Not Taken

Yogi Anand, D.Eng, P.E.       Google Spreadsheet    Post  #695   Aug 14, 2012     www.energyefficientbuild.com.

user B-House said: (http://productforums.google.com/forum/?zx=76albpq7qu02#!category-topic/docs/spreadsheets/_2mcpQHtUOU%5B1-25%5D)
Excluding Text when using ArrayFormula for Average in Spreadsheet
I am trying to create a google form to track a student's GPA. We have 4 classes and I used this formula 

=ArrayFormula( (D2:D+E2:E+F2:F+G2:G) / 4 )The problem that I have is that some students do not take 4 courses. I used N/A is an option on the google form for this instance. The ArrayFormula will not exclude N/A when calculating the average. I need a formula to ignore the N/A and divide by the appropriate number of numerical responses in these circumstances. I hope that this makes sense. I included the link and it should be editable. I appreciate the help!

https://docs.google.com/spreadsheet/ccc?key=0Agi0HENAQ7xLdDFrY0hLeXpIRHpYT0hid2NEcVpkZFE

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following is a solution to the problem