Doesn't it sounds like:
You take a 10kg of rice, you take out each grain of rice very
carefully, one by one, into an empty bag until all the rice from
the 10kg bag is transferred over.
The you take the new 10kg of rice, take out each grain of rice very
carefully, one by one, into the original bag until all the rice is
transferred back again.
the number of grain of rice is still the same.
