A plane leaves an airport traveling at 400 mph in the direction N 45° E. A wind is blowing at 40 mph in the direction N 45° W. What is the ground speed of the plane?

The plane’s direction, N 45° E, and the wind’s direction, N 45° W, are 90° apart. Their velocity vectors are perpendicular, so the ground speed is √(400² + 40²) = √161,600 ≈ 402 mph. The correct choice is 402 mph.

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