SOLUTION: A man travel 20 km at 40 km/h ,10km at 30 km pH and 30 km at 60 km pH determine the average speed?

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Question 895508: A man travel 20 km at 40 km/h ,10km at 30 km pH and 30 km at 60 km pH determine the average speed?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
A man travels 20 km at 40 km/h, 10km at 30 km pH, and 30 km at 60 km pH
determine the average speed?
:
Total distance = 20 + 10 + 30 = 60 km
Let a = the average speed of the whole trip
:
Write a time equation; time = dist/speed
20%2F40 + 10%2F30 + 30%2F60 = 60%2Fa
multiply equation by 120a, cancel the denominators and you have
(3a(20) + 4a(10) + 2a(30) = 120(60)
60a + 40a + 60a = 7200
160a = 7200
a = 7200/160
a = 45 km/hr is the average speed
:
:
Check this by finding the time
20%2F40 + 10%2F30 + 30%2F60 = 60%2F45
.5 + .33 + .5 = 1.33