What die type is used by the most tabletop role-playing games?

d4 d6 d8 d10 d12 d20

What is the average roll value of a d6?

2 2.5 3 3.5 4 4.5 5 5.5 6

What is the average roll of value of an exploding d6? (A d6 in which you roll again and add the result whenever a 6 is rolled on the d6 continuing until not a 6 is rolled)

2.5 3 3.5 4 4.5 5 5.5 6 6.5 7

Which of these systems uses d100 to determine success?

Dark Heresy Dungeons and Dragons World of Darkness Rifts Savage Worlds Shadowrun

Which system uses the standard polyhedral dice to determine success?

Dark Heresy Dungeons and Dragons World of Darkness Rifts Savage Worlds Shadowrun