Algebra
posted by Al .
How long does it take a care traveling 100 mph to catch up to a car traveling 80 mph

Depends how far back the faster car was.
Not enough data. 
Leaves 2 minutes after the car at 80 mph passes it

The car traveling 100 mph states from a complete stop

Key point:
When the faster catches the slower , they both went the same distance
let that distance be x miles
time for faster car = x/100
time for slower car = x/80
x/80  x/100 = 2/60
x/400 = 1/30
30x = 400
x = 40/3 miles
so time for faster car to go the 40/3 miles to catch the slower car
= (40/3) / 100 = .13333.. hr
= 8 minutes
check:
time for slower car
= (40/3) / 80 = .166666 hrs
= 10 minutes, for a difference of 2 minutes 
Thanks!