Thread: probability

a pair of dice is rolled together till a sum of 6 or 8 is obtained.find the probability that 6 comes before 8.

Since 6 and 8 are equally likely on any one roll, the probability that "6 comes before an 8" (which means that the sequence of rolls terminate on a roll of 6, not 8) is exactly the same as "8 comes before a 6". Since one of those two must happen by the rules of this problem, their sum must be 1: each is equal to 1/2.

Hello, psparmar!

There is an "intuitive" solution for this.

A pair of dice is rolled together till a sum of 6 or 8 is obtained.
Find the probability that 6 comes before 8.

We find that: .

Their probabilities are equal.
Either event is equally likely to happen.

Therefore, the probability that a sum of 6 precedes a sum of 8 is: .