There are five possibilities for writing X: 3, 4, 5, 6, 7;
Probability p (x = 3) =1/6;
p(x = 4)= 1/6;
p(x = 5)= 2/6 = 1/3;
p(x = 6)= 1/6;
p(x = 7)= 1/6;
Expected ex = 3 *1/6+4 *1/6+5 *1/3+6 *1/6 = 5;