X, Y and Z each try independently to solve a problem. If their individual probabilities for success are \frac{1}{4}, \frac{1}{2} and \frac{5}{8}, respectively, what is the probability that X and Y, but not Z, will solve the problem?
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A\frac{11}{8}
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B\frac{7}{8}
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C\frac{9}{64}
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D\frac{5}{64}
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E\frac{3}{64}
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正确答案: E