You have been abducted by terrorists and blindfolded. They sit you down at a table and tell you that if you can solve two puzzles then they will let you go.
There is a deck of 52 cards on the table in front of you. Ten cards in the deck are face-up and the rest are face-down (the face-up cards are distributed randomly within the deck). Split the deck into two stacks (of possibly unequal sizes) such that each stack has an equal number of face-up cards.
On one side of the table there are five dice which add up to 15. On the other side of the table there are another five dice which add up to 13. You don't know which side is which. Move some dice around so that the two sides of the table have equal sums.