Suppose that a pair of 7 sided dice is tossed. What is the expected value of the sum?

IF such dice exist, and

IF each die is numbered from 1 to 7, and

IF each die is fair

then

expected value of each die is 7/2=3.5, and

by the rule of sum of random variables,

E[x]+E[y]=E[x+y],

then

expected value of the sum is 3.5+3.5 = 7.

Note: the platonic solids (convex regular polyhedrons) that can be used as fair dice are

tetrahedron (4 faces)

hexahedron (6 faces)

octahedron (8 faces)

dodecahedron (10 faces)

icosahedron (20 faces)

All of these dice exist in the market.