Increment column address while copying formula down

I am creating a training document for work; the sheet I'm creating is a summary sheet which works out how many people answered questions correctly, incorrectly (bringing in from another sheet), number of questions answered and percentage of correct answers.

Looks like:
Correct: =COUNTIF(sheet1!E2:E36,"correct")
Incorrect: =COUNTIF(sheet1!E2:E36,"incorrect")
Number of questions answered: =SUM(C4+C5) (correct+incorrect)
Percentage right: =SUM(C4/C6) (correct/number answered)

I need to drag these 4 formulas down into another 400+rows, however in the correct and incorrect formulas I need it to keep the 2:36 but change the e to f, g, h, etc…
Is this possible? Thanks