At noon, ship A is 90 km west of ship B. Ship A is sailing south at 20 km/h and ship B is sailing north at 10 km/h

sailing-north

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At noon, ship A is 90 km west of ship B. Ship A is sailing south at 20 km/h and ship B is sailing north at 10 km/h. How fast is the distance between the ships changing at 4:00 PM?

Answer:

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