How should a special rent discount be divided among roomies?

Okay, so my wife and I recently moved in with a couple of friends so we could all have a lower rent payment in a nicer , larger place.

As it stands, we’ve worked it out to where we pay by the bedroom. My wife and I have the master bedroom, so we collectively pay 40% of the rent, while each other other two roommates individually pay %30 each.

But one of our roommates got 5% off the total price of rent on a monthly basis from a student discount. So every month, the rent will be 5% less total.

This roommate claims he should deduct the entire discount amount from his existing 30% portion of rent. But is that really the fair way to do it? How would you take care of this if you were in this position? Would you share the discount? Would you be a stickler? What’s the proper mathematical way to fairly apply this discount only to the student’s rent?

Also bear in mind that my wife and I may not have a student discount to apply, but we have other contributions, including a washer and dryer – without which the others would still be schlepping their clothes to the laundromat every week.

What do we do?