physics
posted by mary otto .
to qualify for a race, a car must average 350 km/hr for four laps. If a driver averages 285 km/hr for the first two laps, what average speed must be achieved for the final two laps in order to qualify?

avg speed=distance/time
350=4laps/(time2+time4)
time for first two time2=distance/285=2laps/285
time for last two laps=2laps/V
350=4/(2/285+2/V)
2/285+2/V=4/350
2/v=4/3502/285
1/V=2/3501/285
V=350*285/(2*285350) and you can finish it. 
453.41