The tub is full ...
What must be the case, so that the water drains off more quickly? When I sit in the tub or when I stand outside the tub?
Answer:
b) The water will drain off more slowly, if I sit in the tub, because with my body I am pushing against the flow direction of the water.
c) It always takes the same time because always the same amount of water has to drain off.
d) The water will drain off more quickly, if nobody is sitting in the tub. Because of the lower water level, the distance of the water to the drain is shorter.