Answer:
12 mph
Step-by-step explanation:
The relationship between jogging speed and walking speed means the time it takes to walk 4 miles is the same as the time it takes to jog 8 miles. Then the total travel time (0.75 h) is the time it would take to jog 1+8 = 9 miles. The jogging speed is ...
(9 mi)(.75 h) = 12 mi/h . . . average jogging speed
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Check
1 mile will take (1 mi)/(12 mi/h) = 1/12 h to jog.
4 miles will take (4 mi)/(6 mi/h) = 4/6 = 8/12 h to walk.
The total travel time is (1/12 +8/12) h = 9/12 h = 3/4 h. (answer checks OK)
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Comment on the problem
Olympic race-walking speed is on the order of 7.7 mi/h, so John's walking speed of 6 mi/h should be considered quite a bit faster than normal. The fastest marathon ever run is on the order of a bit more than 12 mi/h, so John's jogging speed is also quite a bit faster than normal. No wonder he got tired.
