Question
John can jog twice as fast as he can walk. He was able to jog the first 5 miles to his grandmother's house, but then he tired
John can jog twice as fast as he can walk. He was able to jog the first 5 miles to his grandmother's house, but then he tired and walked the remaining 2 miles. If the total trip took 0.9 hours, then what was his average jogging speed?
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Koala Tutor
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Let W be the walking speed.
Jogging speed = 2W
The total time jogging is 5 / (2W).
Walking time = 2 / W
5 / (2W) + 2 / W = 0.9
Multiply through the equation by 2W*W, we get 5W + 4 = 0.9(2W^2)
5W + 4 = 1.8W^2
1.8W^2 - 5W - 4=0
0.9W^2 - 2.5W - 2 = 0
0.9(W - 2)(W + 1.11) = 0
W = 2 or -1.11; since jogging speed should be positive we choose W = 2;
Therefore, his average jogging speed is 2 * 2 = <<2*2=4>>4 miles per hour. Answer: \boxed{4}.
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