If you mean a commercial passenger jet you are way off. Their average speed is about 500 knots or around 600 mph. It is due to the high altitude (around 35 to 45 thousand feet) that makes the ground seem to be going by so slow. That is an optical illusion caused by several factors, but believe me, if they were only going about 80 mph, it would take well over an hour to get from one airport to another that was only a hundred miles away.

In reference to the above answer, he's right. I am an X-Air Force jet jock of the Korean era and between the F86, F89, and F102's that I flew, typical air speed at take off was around 180 knots for all of them. I'll let you do the math to convert that to mph.