A scooterist goes to a place of 20km/hr and return at a speed of 30mm/hr. Find the average speed in km/hr for the entire ?

1 Answer
MeneerNask · Nam D.
Mar 6, 2018

We can do this in different ways. I like this one:

Explanation:

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=(3D)/60+(2D)/60=(5D)/60=D/12#
for a distance of #2D#

Average speed will be #2DdivD/12=2cancelDxx12/(cancelD)=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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