9514 1404 393
Answer:
after 1 hour
Step-by-step explanation:
One of the ways to solve this is to look at the separation of the boats after 1 hour. One is 30 miles north and the other is 40 miles east of the dock. The distance between them is the hypotenuse of the right triangle with legs 30 and 40 miles:
d = √(30² +40²) = √(900 +1600) = √2500 = 50
The boats are 50 miles apart after 1 hour.
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Additional comment
Had we been concerned with a different distance, we could use the separation speed of 50 mi/hour to determine the time.
