How will you half fill a random shape bottle ?

Question

You have a bottle of random shape and you want to fill HALF of it with water. You have available only a pump with unlimited water. Nothing else. How will you fill it?

Answer 1

Very Tricky
Put some water in the bottle and close the cover very tightly and put a mark on the water label. Now if we reverse the bottle the water label should be equal to the mark which we put earlier if it is half of the bottle. Now keep adjusting water till you find half bottle.

Answer 2

First open the pump and FULLY fill the bottle and note the time taken to fill the whole bottle.
Then, poor out the water from the bottle, and this time open the pump for half the time you used to fill the whole bottle.

The bottle will be HALF filled.