a scooter is goes to a place at a speed of 20 km per hour and returns from there at a speed of 30 km per hour find the average speed of speed in the kilometre per hour for the entire journey
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Answer:
Since we don't know the distance we will call this
D
.
The time for the out trip is
D
20
and the return trip will take
D
30
(in hours)
The total time will be
t
=
D
20
+
D
30
=
3
D
60
+
2
D
60
=
5
D
60
=
D
12
for a distance of
2
D
Average speed will be
2
D
÷
D
12
=
2
D
×
12
D
=
24
km/h
.
Note:
Since this works for all distances (they cancel out in the end), you just could also have picked any convenient distance, like
60
km
:
Out
3
hours, home
2
hours,
120
km
in
5
hours, same result.
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