when finding conditional frequency, how do you know if you should put the row total or column total in the denominator?

Usually, the first term mentioned for the conditional frequency, you put the column or row total in the denominator, with the data being observed in the numerator. For example of all the people that like skateboards, how many like snowmobiles? Would be 80/125 or if I asked of all the people that liked snowmobiles how many like snowboards would be 80/105. 

Sin(a)+cos(a)+cot(a)-1=2(csc(x)+1)