InfoPath Dev

What I'd like to do is have txtField1 in my example below, in first row and last row only be equal to 75% of the value of txtField1 in the rows between the 1st and last rows.  I am determining which txtField1 value to change in a row based on the value of its corresponding  datepicker1 value.  If datepicker1 value equals a date value of another field (outside this particular repeating table, say datepicker2) then calculate a different value for txtField1.

Is this possible to do in a repeating table when the variables are the same for all rows?  Or must I create a new variable and exclude it from the repeating table to accomplish this?  I can get the formula to work but it changes all txtField1's no matter what the date condition is so I can't tell if it's not working because I'm putting my datepicker conditions in the wrong place or because the fact that txtField1 is in a repeating table....??

Example - 1 repeating table (all fields are same in each row)

  Row 1 controls are datepicker1,  txtField1= (.75 * txField4),   txtField2 and txtField3. (each txtField is decimal data type).
  Row 2 controls are datepicker1,  txtField1 = (txtField4),         txtField2 and txtField3. (each txtField is decimal data type).
  Row 3 controls are datepicker1,  txtField1 = (txtField4),         txtField2 and txtField3. (each txtField is decimal data type).
  Row 4 controls are datepicker1,  txtField1= (.75 * txtField4),  txtField2 and txtField3. (each txtField is decimal data type).

Update:  This can be done.  I realized there are several ways to approach it.  What I ended up doing was adding a check box control to the repeating table to indicate TRUE if it was a row I wanted to effect the value change in.  The problem I had getting it to work stemmed more from forgetting to add a couple other rules/conditions that were necessary.  I wasn't being specific enough.