The rocket that carried the Curiosity Rover to Mars traveled at a speed of 21,000 miles per hour. What is this speed to the nearest mile per second?

There are 3,600 seconds in an hour, so convert miles per hour to miles per second by dividing 21,000 by 3,600. That is about 5.83 miles per second, which rounds to 6 miles per second. The correct choice is A, 6 miles per second.

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