At 9:00 on a saturday morning, 2 bicyclists heading in opposite directions pass each other on a bicycle path. The bicyclist heading north is riding 6 km/hour faster than the bicyclist heading south. At 10:15, they are 42.5km apart. Find the two bicyclists' rates.

Question

phi · Answer

At 9:00  2 bicyclists pass each other
At 10:15, they are 42.5km apart

from the time they passed each other, how long have the biked by 10:15?

do you know 
speed*time= distance
?
you know time (figured out above) and distance (given in the problem)
so you can find "opening speed" (how fast the 2 are moving away from each other)

let the speed of the biker going south be "S"
the guy going north goes 6 km/hr faster:  S+6  

the opening speed must equal the sum of both biker's speed: S+S+6