ABSTRACT
Th e ratio of all the black parts to all the white parts of the cube’s surface is 1:1.
Th e two pentominoes that should be exchanged are the upper-left and the lower-right ones. When they are exchanged and placed as shown, the original pattern is restored: the upper row of pentominoes is A, B, and C; the middle 20 dots are the next 20 undisclosed letters of the English alphabet; and the lower row of pentominoes is X, Y, and Z.
