SOLUTION: A boy cycles from his house to a friend's house at 20 km/h and home again at 25 km/h. If his round trip takes 9/10 of an hour, how far is it to his friend's house?

Question 207883: A boy cycles from his house to a friend's house at 20 km/h and home again at 25 km/h. If his round trip takes 9/10 of an hour, how far is it to his friend's house?
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
A boy cycles from his house to a friend's house at 20 km/h and home again at 25 km/h. If his round trip takes 9/10 of an hour, how far is it to his friend's house?
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Use d = rt
t = d/r = 54 minutes
54 = d/20 + d/25
54 = (5d + 4d)/100
9d = 5400
d = 600 (km/hr times 60, since we used minutes)
c = 10 km
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Check: 10 km at 20kph --> 30 minutes
10 km at 25 kph --> 24 minutes
Total 54 minutes
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