This works if your data is always 1 and 0.

Declare @table table(id int, colA int, colb int, colc int)

Insert into @table

Select

1 , 1 , 1 , 0

Union All

Select

2, 0 , 1 , 1

Union All

Select

3 , 0, 0 , 1

Union All

Select

4 , 1 , 1, 1

Union All

Select

5 , 1, 1 , 0

Select

Sum(cola)/Convert(Float, Count(id)),

Sum(colb)/Convert(Float, Count(id)),

Sum(Colc)/Convert(Float, Count(id))

From

@table

Will there ever be values other than 1 or 0? If so how do you know what value you are trying to find the percentage for?