Question 966597
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R=rate on the way to the mountains. Since distance was the same in both directions, rate going x time going = rate returning x time returning or:
R(12 hours)=(R+20mph)(8 hours)
12R hours=8R hours + 160 miles Subtract 8R hours from each side.
4R hours=160 miles Divide each side by 4 hours.
R=40 miles/hour Tony's average speed on the way to the mountains was 40 mph.
The trip took 12 hours at 40 miles per hour, so distance was:
(12 hours)(40 mph)=480 miles
ANSWER: Tony lives 480 miles from the mountains.
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CHECK: 
Return trip at 20mph faster took 8 hours:
480 miles/(40mph+20mph)=8 hours
480 miles/60 mph=8 hours
8 hours=8 hours