Suppose the Yes/No fields are named like f1, f2, f3, ..., f10
SELECT Site, (IIf(f1, 1, 0) + IIf(f2, 1, 0) + IIf(f3, 1, 0) + IIf(f4, 1, 0) + IIf(f5, 1, 0) + IIf(f6, 1, 0) + IIf(f7, 1, 0) + IIf(f8, 1, 0) + IIf(f9, 1, 0) + IIf(f10, 1, 0))/10 As CorrectPercent FROM QuizResults