Calculating Average Speed

SydneyRoverP6B

SydneyRoverP6B

Well-Known Member
Staff member
We all like to take our Rovers on a long trip every now and then, so calculating our average speed for the trip might be something we might like to do on occassions.

So here is a little question to ponder and to post your answers to.

A driver sets out on a journey. For the first half of the distance she drives at a leisurely pace of 60km/h; she drives the second half at 120km/h. What is her avergae speed for the trip?

Ron.
 
80 km/h - 120 is exactly double 60 so for e.g 240 km are completed in 3 hours. 240/3 = 80.

As it's a ratio the actual distance covered doesnt matter....
 
Good one!

In y hours, she will have done 60y km for the first half. In the second half, as she is going at double the speed, she does 60y km in y/2 hours

Mean = (60y + 60y) /(y + y/2) = 120y/(1.5)y

The y's cancel out....

Mean = 120/1.5 = 240/3 = 80 km/h
 
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