I am trying to work out this statement but can't get anywhere. 

From what I have found so far, I think I need to use an `nullif` clause for each divisor, but when I try and do this it still does not work.

Here is the statement with no `nullif`'s that produces a divide by zero error.

```
(1 - (1 - (x1.hup / (x1.hup / (x1.dp / 100)))) / (1 - (x2.sdp / 100)))

```