I got the fifth post!

I'll get that blasted Road Runner yet! Argggh!

Coyote

No...it just takes away from all of the things I have to
say...hehehe..just kidding...I like the logic problems but they do need
their own deal...remember this is a communitity and Russ and Chris
are doing everything they can to make this the best site on the web!

And doing a hell of a job of it too!!

Dave
Proud Pawn Star

it can't be done, because, as has been shown, your speed would have to be such that you could cover the distance in zero time!
if you come back at 120, your return-trip time would be 1/4 of your out-trip time, but your _average_ is only 48 mph!
try 150. now your average speed is only fifty.
it doesn't matter what the speeds involved are--there is no way you wil ever be able to average twice the speed on a return trip over the same distance!

Distance X. Time on the way there X/30. Average 60. Total distance 2X. Total time 2X/60 = X/30.

Time for the way back X/30 - X/30 = 0

Originally posted by Acolyte
"Both distances are the same."

Joke? If so, you can explain the flaw in this reasoning better than I am about to.

If not, the flaw is that, taking 'average' to mean 'mean', average speed is the sum of each
speed multiplied by the TIME spent at that speed, divided by total TIME. If instead we
performed the calculation using DISTANCE instead ...[text shortened]... those can never be higher than
30mph unless you take a detour. But that's another matter...

To those who think the answer is 90 or 120:

Say its 30 miles to work, I drive there at 30mph, it takes me 1 hr

I drive back at:
a) 90 mph, now its taken me 1 hr and 20 mins to go 60 miles
b) 120 mph, now its taken me 1 hr and 15 mins to go 60 miles
c) infinity mph, now its taken me 1 hr to go 60 miles (but I've used a lot of fuel)

I think only c is an average speed of 60 miles per hour.

Crikey - this thread, long time, no see.

As I set this poser, I guess I should officially state that the answer, of course, is that it can't be done. As for whether it can be done at infinity MPH I don't know - I guess that this would be infinitely close to an average of 60mph, but would it be spot on? Too hard for my brain.

It can't be done, because, as has been said many times already, if you want to average double the speed of your outward trip, you would have to return in no time at all, therefore travelling twice the distance in the same amount of time.

-Chris