Nine heart cards from an ordinary deck can easily be arranged to form a magic square so that each row, column and main diagonal has the largest possible constant sum, 27.
(Jacks count 11, queens 12, kings 13.)

Drop the requirement that each value must be different.
Allowing duplicate values, what is the largest constant sum for an order-3 magic square that can be formed with nine cards taken from a deck?

Attributed to the great Martin Gardner.