[Prof. Templeton]

You just bought a new sportscar, and you want to bring it to the racetrack to see how it will perform. The track is very busy and will only allow 2 laps. Since it's your first time at the track you take it easy on the first lap and average 40 Miles per hour.

How fast would you have to go on the second lap to end the day with an average of 80 miles per hour?

[Guest]

120 mph?

[Guest]

The obvious (but incorrect answer) would be 120 mph, but that's basing the answer on distance rather than time. But since the time factor changes (though distance remains the same), 120mph cannot work.

The truth is that it's impossible, as per the post from several days ago asking a similar average

[Prime]

Nice algebra problem.

It's not possible to make average speed 80 mph after you went half way at 40 mph.

If your average speed is 80 mph, you travel twice the distance in the same amount of time compared to 40 mph. Two laps is twice the distance compared to one lap. Thus if you can travel second lap in zero time, your average speed would be 80 mph. But you cannot do it, unless you travel at the speed of light.

[Prof. Templeton]

Nice algebra problem.

It's not possible to make average speed 80 mph after you went half way at 40 mph.

If your average speed is 80 mph, you travel twice the distance in the same amount of time compared to 40 mph. Two laps is twice the distance compared to one lap. Thus if you can travel second lap in zero time, your average speed would be 80 mph. But you cannot do it, unless you travel at the speed of light.

I bet you could get in more laps that way without the track officials noticing.

[Guest]

120?

40+120/2=80

Edited August 19, 2008 by javoie

[rookie1ja]

one of my favorites ... I admit searching for this one is difficult, however, it's already posted (by me ) with long discussion

thread locked