Tag Archives: probability

Mystery Dice Question

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

Hitting the Target

Here is a problem from the UKMT Senior (17-18 year-old) Mathematics Challenge for 2012:

“Tom and Geri have a competition. Initially, each player has one attempt at hitting a target. If one player hits the target and the other does not then the successful player wins. If both players hit the target, or if both players miss the target, then each has another attempt, with the same rules applying. If the probability of Tom hitting the target is always 4/5 and the probability of Geri hitting the target is always 2/3, what is the probability that Tom wins the competition?

______A 4/15______B 8/15______C 2/3______D 4/5______E 13/15”


See Hitting the Target for solutions.