Dividing by Zero

I am writing a program in Excel to calculate my investigators' monthly totals.

If they are assigned 4 cases and clear 2, their clearance rate = 50%
If they are assigned 2 cases and clear 4 (2 came from previous month), their clearance rate = 200%
If they are assigned 2 and clear 0, I use the "IF" command and get a 0% answer.

Problem:
If they are assigned 0 and clear 2 (the 2 are from the previous month), what formula can I use to give them credit for the clearance???? If it is any # other than "0", it works!!!

wouldn't cases cleared times 50% give you the answer???

shg has provided for a very effective approach. If, however, you feel uncomfortable moving away from cases closed, take a look at the attached

Thank you, that might work!!!!