In 15-3 = 12 seconds, he passes 20 - 5 = 15 floors. If each floor is 3 meters, he covers a distance of 45 meters. So his speed is 45/12 = 15/4 = 3.75 m/s.

Of course if each floor is 3 meters high, it's not clear what it means to 'pass a floor' (when during the 3 meters do we consider the floor to have been 'passed'?), but I imagine the interpretation above is what is intended.

BTGmoderatorLU wrote:Source: Economist GMAT

Mr. Wayne bungee jumps from the top of a building straight to the ground at a constant speed. 3 seconds after he starts plummeting he passes the 20th floor. 15 seconds after he starts plummeting he passes the 5th floor. Each floor is 3 meters high. What is Mr. Wayne's speed in meters per second?

A. 3
B. 3.75
C. 4
D. 4.25
E. 5

The OA is B

We can see that Mr. Wayne is descending |5 - 20|/|15 - 3| = 15/12 = 5/4 floors per second. Since each floor is 3 meters, he's descending 3 x 5/4 = 15/4 = 3.75 meters per second.

Answer: B