That's because when you divide the distance by time, you get the average speed...

However, the question is, did Robin exceed the 55 mph speed limit?

So the average speed has no significance here

We require the peak speed!

So using statement 1 and 2:

Robin drove for 2 hours and covered a distance of 100 miles:

Case 1

If Robin drove at 60 mph for the first hour, distance = 60 miles

If Robin drove at 40 mph for the next hour, distance = 40 miles

Total Distance = 100

Total time = 2 hrs

Did she exceed the speed limit? YES!

Case 2:

If Robin drove at 50 mph for 2 hours, distance = 100 miles

Total Distance = 100

Total Time = 2 hrs

Did she Exceed the speed limit? NO!

Thus, insufficient!

_________________

Mission: Be a force of good and make a positive difference to every life I touch!

From 650 to 710 to 750 - My Tryst With GMAT [Experience Thread]