"Okay," says Galileo\. "I measured this tower to be 45 meters tall\. Now, if air resistance is 0, after 3 seconds the ball should be moving downward at a speed of 9\.8 \* 3 = 29\.4 meters per second\. That speed increases continuously over the 3 seconds, so the ball's average speed will have been 29\.4 / 2 = 14\.7 meters per second\. And if the ball moves at an average speed of 14\.7 meters per second, for 3 seconds, it will travel downward 44\.1 meters\. So the ball should take just a little more than 3 seconds to fall 45 meters\. Like, an additional 1/29th of a second or so\."

More explanation as how to calculate average velocity?