A pilot flew a 400-mile flight in 2.5 hours flying into the wind. Flying the same rate and with the same wind speed, the return trip took only 2 hours, with a tailwind. What was the speed of the wind?

Flying into the wind, the plane’s ground speed was 400 ÷ 2.5 = 160 miles per hour. With the wind, it was 400 ÷ 2 = 200 miles per hour; the difference, 40 miles per hour, is twice the wind speed, so the wind was 40 ÷ 2 = 20 miles per hour. The correct choice is D, 20.

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