Question

Mario and sheen a were thirsty after a long bike ride, so they stopped to get a glass of lemonade. Their friend Andy was selling lemonade. He poured the lemonade into the two glasse. Before they start drinking sheena who had the shorter glass complained that she had paid the same amount of money as Mario but didn't get as much lemonade. Andy insisted that they had the same amount.
How Andy could prove his two customers got the same amount of lemonade

Answer 1

use a third container.

Pour lemonade from one glass into it and mark its height.

Then do the same with the other glass.

If the height is the same, the glasses contain the same volume of drink.