A Mean Question

Algebra Level 2

A car travelled New York to New Jersey at 40 mph. The same car travelled back from New Jersey to New York at 60 mph. Calculate the car's average speed in it's entire trip.


The answer is 48.

Edgar de Asis Jr. by Edgar de Asis Jr. , 25, Philippines

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2 solutions

In general, when the length of the trips are the same, the average speed will be the harmonic mean of the respective speeds..........so avarage speed= 2 / (1/u + 1/u' )

2 Helpful 0 Interesting 0 Brilliant 0 Confused

You can also the formulae 2xy/x+y

Anuj Shikarkhane - 6 years, 10 months ago

Please, in what situations do we use the harmonic, geometric, and arithmetic mean

Nehemiah Osei - 5 years, 8 months ago

t i m e = d i s t a n c e s p e e d time=\dfrac{distance}{speed}

Let d d be the distance from New York to New Jersey. We have,

a v e r a g e s p e e d = t o t a l d i s t a n c e t o t a l t i m e = d + d d 40 + d 60 = 2 d d 24 = 2 d ( 24 d ) = 48 average~speed=\dfrac{total~distance}{total~time}=\dfrac{d+d}{\dfrac{d}{40}+\dfrac{d}{60}}=\dfrac{2d}{\dfrac{d}{24}}=2d\left(\dfrac{24}{d}\right)=48

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