Mystery of the balls - Henrique has two urns. The first urn contains only black balls and the second only white balls. Henrique removed a number of balls from the first urn and placed them in the second. Then he removed the same number of balls from the second urn and placed them in the first. After this, is the number of white balls in the first urn greater than, less than, or equal to the number of black balls in the second urn?