ExplanationTo solve this question Plug In. Since the question deals with percents, try 100. If the F train arrives 100 times per day, then the B will arrive 10% fewer times than 100:

\(B = (1- \frac{10}{100}) \times 100=90\) times,

and the Q will arrive 30% fewer times than 90: \(Q = (1 - 30/100) B = ( \frac{70}{30})90 = 63\) times.

Translating the question “the Q train’s frequency is what percentage of the F train’s” gives \(Q = \frac{x}{100} \times F\) or \(x = 63\).

Which means that the Q’s frequency is 63% of the F’s. The correct answer is choice (D).

Hence option D is correct!
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Sandy

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