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bettatantalo
Jenny drove to the gym with an average speed of 60 miles per hour. On her way back she drove the same route with an average speed of 80 miles per hour. What was er average speed for the whole trip in mph?

a) 60

b) 68

c) 68 4/7

d) 70

e) 74 3/8

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If the distance from home to gym is D, then total distance =2D
time from Home to Gym T1=D/60
time from Gym to home T2=D/80

average speed = total distance/(T1+T2)
= 2D/(D/60+D80)
=68 4/7
answer is C
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bettatantalo
Jenny drove to the gym with an average speed of 60 miles per hour. On her way back she drove the same route with an average speed of 80 miles per hour. What was er average speed for the whole trip in mph?

a) 60

b) 68

c) 68 4/7

d) 70

e) 74 3/8

We can let the distance each way = 240 miles and use the formula: average rate = total distance/total time:

average rate = 480/(4 + 3) = 480/7 = 68 4/7

Answer: C
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Average speed from her home to the gym = 60mph
Therefore time taken from her home to the gym = 240/60 = 4 hours
Average speed from the gym to her home = 80mph
Therefore time taken from the gym to her home = 240/80 = 3 hours
Total distance = 480
total time taken = 7 hours
Average speed = Total Distance/Total Time = 480/7= 68 4/7
Therefore C is the correct answer
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chetan2u Can please explain how did you derive 2d ?
Average speed = 2d/(7d/240)=480/7
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VERBAL1
chetan2u Can please explain how did you derive 2d ?
Average speed = 2d/(7d/240)=480/7

Hi

d is distance between two places, but she travels Both ways that is d+d
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