Where is my mistake ?

We can use this formula to find the average rate of the the trip :

2 [ R₁ * R₂] /  [ R₁ + R₂ ]    where R₁ and R₂  are the different rates over the same distance ....so we have

2[ 90 * 60] / [ 90 + 60] =

2[ 5400]/ [ 150]  =

72 mph

So ......the average rate * 6 hrs  = twice the distance......so divide this by 2 and we have 

72 * 6 / 2 =

72 *  3  =

216 miles  !!!

I so wish i could help you! You're a very nice person :)

But i dont know how to do it..

I'm sorry :(

thanks Hayley! :)

But can it be determined without puting any distance

Steve travels from NYC to Boston at 90mph and returns to NYC at 60mph taking 6 hours total for the round-trip without stopping. What is the distance between NYC and Boston ?

Let the distance be d

Let x be the time to get there and y be the time to get back

x+y=6

y=(6-x)

speed=distance/time

90=d/x                60=d/(6-x)

90x=d                 60(6-x)=d

x=d/90 (1)           6-x = d/60

                           x=6 -  d/60 (2)

so

\(\frac{d}{90}=6-\frac{d}{60}\\~\\ 180*\frac{d}{90}=180*(6-\frac{d}{60})\\~\\ 2d=1080-3d\\~\\ 5d=1080\\~\\ d=216\; miles\)

Hang on a minute Solveit.  

What do you mean "without putting any distance" ?    

Thanks everybody, i understood everithing! exuse me for taking your times!

My question it was wrong:  2 [ R1 * R2]  and d all of it distances (just a stupid question:)