Don't assume they know, because most folks don't. When you do the prediction by showing them the top and bottom of the dice and then say 14 they are really surprised. Most people do not know that the top and bottom of the die equal 7.
I have practiced in front of an audience by just using one die after a little routine I do to predict the numbers - 14 - on both sides. It is kinda difficult to get the hang of.
