This is a relatively simple probability question from Presh Talwalkar that becomes an excuse to describe a powerful tool.

“Amazon’s Mystery Dice Interview Question

You are given a normal die and a blank die. (Each die is six-sided and equally likely to show each face). Label the blank die using the numbers 0 to 6 so that when you roll the two die the sum shows each whole number from 1 to 12 with equal chance. You can use a number more than once, or not at all, so you could label the faces 1, 2, 3, 4, 4, 5. But you do have to label all six faces of the blank die.”

See the Mystery Dice Question