How much time did it take a certain car to travel 400 kilometers?
1) The car traveled the first 200 kilometers in 2.5 hours.
2) If the car’s average speed had been 20 kilometers per hours greater than it was, it would have traveled the 400 kilometers in 1 hours less time than it did.
1) insufficient - no info about second 200 km
400/(t-1)-400/t = 20 -> t^2-t-20 = 0 -> t1=-4 (can't be negative), t2 = 5