You are a surgeon who has to perform 3 operations today, but you only have 2 pairs of gloves (a and b) to perform the operations. Each of the people you are performing surgery on are infectious so you cannot touch any of them or their bodily fluids and they can't touch each other's bodily fluids. How do you perform all 3 operations with only 2 pairs of gloves?
You put pair a on and put pair b on top of pair a and perform 1 surgery. You then remove pair b and perform another surgery. Finally you take pair b and put it over pair a inside out and perform the final surgery.