Race Track!

[AC_A340-500]

OK, pretend that you're at a race track, let's say the Nuerburgring. This race track has a length of 2 kilometers (OK, the real Nuerburgring is longer, but go along with me here). Your assignment is to take your car to this race track, and to complete two (2) laps on it, averaging a speed of 120 km/h for both laps . You start out, and after completing the first lap , you realize that your average speed so far has only been 60 km/h.

Here's the question:

What speed do you have to average on the second (2nd) lap, in order to attain the goal of averaging 120 km/h for both laps?

[LH 340-600]

You would have to be really fast. To complet the first 2 km with an average speed of 60 km/h you need the same as you need to complete 4 km with 120 km/h.

[Richard]

Second lap average would have to be 180km/h. I think.

Here's how I did it.

So the avg. of two laps would be 120, this means that the total speeds for each lap added together would make 240. seeing that the first lap was done in 60, then minusing that from 240, you'd have 180 which would be how fast you need to go on the second trip.

kinda like that average equation in mathematics but worked backwards.

first value+second value/number of values=average

[AC_A340-500]

hey LH 340-600:

Correct answer! That was quick!

[PK246]

That was nice!

[AC_A340-500]

Just to clarify:

LH A340-600 figured it out first:

After completing the first lap at 60km/h (thereby taking 2 minutes to do so), ALL of the time required to complete 2 laps (4km) at 120km/h (which also requires 2 minutes) is already used up. Therefore, it's impossible to attain an average speed of 120km/h (for both laps) if you complete the first lap at 60km/h.
One can only approach an average of 120km/h for both laps, as the average speed for the second lap approaches infinity.

[LH 340-600]