A plane flies round-trip to Philadelphia. It flies to Philadelphia at 220 miles per hour and back home with a tailwind at 280 miles per hour. If the total flying time takes 6.5 hours, how many miles does the plane fly round trip?

Let d be the one-way distance. The two flight times add to d/220 + d/280 = 6.5, so d(1/220 + 1/280) = 6.5. Solving gives d = 800.8 miles, and the round trip is 2 × 800.8 = 1,601.6 miles. The correct choice is 1,601.6 miles.

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