AMC8 2011 Problem 18

A fair six-sided die is rolled twice. What is the probability that the first number that comes up is greater than or equal to the second number?
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Answer Choices
A. \dfrac{1}{6}
B. \dfrac{5}{12}
C. \dfrac{1}{2}
D. \dfrac{7}{12}
E. \dfrac{5}{6}