Mary and Joe are to throw three dice each. The score is the sum of points on all three dice. If Mary scores \(10\) in

Presumably this question means to talk about 6-sided dice labeled from 1 through 6. When you roll one die, your average roll is 3.5, so when you roll three dice, your average sum will be (3)(3.5) = 10.5. With ordinary dice, you're as likely to roll something above average as you are to roll something below average, so the probability your sum is greater than 10.5, and thus greater than 10, is just 1/2, or as these answer choices are written, 32/64.

The whole question is bizarre for several reasons though. The GMAT never asks questions about dice, since the test doesn't expect test takers to know what dice are -- there are different kinds of dice, and they can be labeled arbitrarily, so any question would need to explain what kind of dice it's talking about.
And when you roll three six-sided dice in order, a total of 6^3 = 216 things can happen. So the answer choices here are mystifying to me for two separate reasons: none of the fractions is reduced, which is almost never true in real GMAT questions (the GMAT wants to reward, not punish, test takers who have the good mathematical habit of reducing fractions immediately), and the denominators are all, bizarrely, 64, which is unrelated to the number of possible outcomes when you roll 3 dice. At first I wondered if the answers were written that way to offer a number theory based solution -- it must be possible to write the correct answer with a denominator of 216, so when we reduce each answer choice, the denominator of the correct answer will need to be a factor of 216, and it's impossible that C or E is correct -- but pursuing that line of reasoning doesn't eliminate enough wrong answers to be worthwhile.