Two fair dice each with at least 6 faces are rolled. On each face of each die is printed a distinct integer from 1 to the number of faces on that die inclusive. The probability of rolling a sum of 7 is equal to the probability of rolling a sum of 10, and the probability of rolling a sum of 13 is . What is the least possible number of faces on the two dice combined?
15
16
17
18
19
