Alan and Dave start at the same point and drive in opposite directions. Alan has one hour head start and drives at 55mph. Dave drives at 65 mph. How long until they are 250 miles apart?

After 1 hr Alan has travelled 55 mi. This means that together they must now travel 195 mi 
starting after 1 hr...
Distance Alan travels: 55t
Distance Dave travels: 65t 
55t+65t = 195 
this gives t=195/120=1 and 5/8 hrs 

so total time is 2 and 5/8 hrs (2 hrs, 37.5 minutes) 


:)