Question: 2014 Winter Final - 23
We roll a pair of fair dice repeatedly and independently, and stop as soon as the sum of the numbers
for the pair is 7. Define the random variable $X$ to be the number of times we roll the dice. (In
one roll, we roll a pair of dice.) What is the expected value of $X$?
(a)
5
(b)
7
(c)
4
(d)
6