Suppose we lay down two cups in front of you. One of the cups is filled with tea and the other one with coffee. Now we ask you to take a spoonful of tea and mix it with the coffee. At this moment, the coffee cup has a mixture of tea and coffee. You have to take that mixture (spoonful) and add it back to the tea.

Can you now tell if the cup of coffee has more tea or the cup of tea has more coffee ?

Hard Lateral Thinking Puzzle

The fact is that both the amounts are same.
After the swap has been done, you must know that the quantity of liquid is same in both the cups as you have taken and mixed a spoonful only in both the cases. So, there is no change in the quantity of the liquids.

No if there is any tea missing from the tea cup, it is now in the coffee cup. Also, since the quantity is same, then the same amount of coffee must be missing from the coffee cup and is now in the tea cup.