Can someone please explain this question's answer to me? Or at least point me to the solution video for it? I saved it in the super quiz

GRE Quant Problem Solving
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It’s in GRE Mini Exam #14.

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Hey! So I think you should check the solution once, because wile calculating the probability of a student getting 70% or more, Greg considers the case of 7,8,and 10, but misses case of 9 correct, which adds another 10/1024. Although it doesn’t change the answer much, just an observation.

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I think he fixed it later on?