
Answer:
2.75
Step-by-step explanation:
Let's start by making a frequency table. If there is one face, you have a 1/12 chance of getting the value--that's what the "frequency" column means.
Face           Frequency
1 Â Â Â Â Â Â Â Â Â Â Â Â Â 3/12
2 Â Â Â Â Â Â Â Â Â Â Â Â Â 3/12
3 Â Â Â Â Â Â Â Â Â Â Â Â Â 1/12
4 Â Â Â Â Â Â Â Â Â Â Â Â Â 4/12
5 Â Â Â Â Â Â Â Â Â Â Â Â Â 1/12
Now to get E(X) we need to multiply each face by the frequency of it occuring and add all these together:
E(X) = 1(3/12) + 2(3/12) + 3(1/12) + 4(4/12) + 5(1/12)
   = 2.75