Rate Problem

[DCJ]

I tend to overcomplicate these so someone please explain

How much time did it take a certain car to travel 400km?

(1) The car traveled the first 200 km in 2.5 hours
(2) If the car's average speed had been 20km/hr greater than it was, it would have traveled the 400km in 1 hour less than it did

[yogami]

IMO B
let the ave speed be x and let the time taken for the 400 km journey be t
so x = 400/t



(1) does not tell us anything about the remaining 200 km so insuff
(2) tells us that x + 20 = 400/(t - 1)

Solving this with the above equation will give us x and t hence suff

[shibal]

IMO B

[cholloway]

found a more helpful answer here: https://www.beatthegmat.com/gmatprep-wor ... t7380.html