SOLUTION: a boy travels with a speed of 30 kmph for first 1/3 journey time during the remaining journey time he travels with a speed 60kmph find the average speed of the boy

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Question 495288: a boy travels with a speed of 30 kmph for first 1/3 journey time during the remaining journey time he travels with a speed 60kmph find the average speed of the boy

Answer by ankor@dixie-net.com(22740) (Show Source):
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a boy travels with a speed of 30 kmph for first 1/3 journey time during the remaining journey time he travels with a speed 60kmph find the average speed of the boy
:
Let t = total time
then
t = time at 30 km/h
and
t = time at 60 km/h
:
Let a = average speed for the journey
:
Write a distance equation: dist = speed * time
:
30km/h dist + 60 km/h dist = total dist
30*t + 60*t = at
We can cancel out the denominators
10t + 20(2t) = at
10t + 40t = at
we don't care about t, divide thru by t and eliminate it
10 + 40 = a
a = 50 km/h is the average speed