Question 550081
With speed, time, and distance problems, you always start with the fundamental distance equation, substitute what you are given, and then solve what's left.
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d = r*t, where d=distance, r=rate, and t=time
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Of course the units of measurement must match.  That is, if distance is given in miles, then the rate must be stated in miles/hour and the time must be in hours.  Otherwise you have to do conversions.
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d = 210 miles (given)
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t = 7 hrs (given)
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r = d/t = 210 miles / 7 hr = 30 mi/hr
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How many miles does he drive at this speed in 5 hours?
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d = 30 miles/hr * 5 hr
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d = 150 miles
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Done.