One disorder would be ''Unisex'' of where a child born can suffer a disorder of where they are born with both male and female genitals on one gender. Doctors and the hospital can surgically remove the extra genital from the child.
The average speed of the bus from Lansing to Detroit is

while the average speed of the bus from Detroit to Lansing is

The distance covered by the bus in the two trips is the same (the distance between the two cities), therefore, the average speed of the round trip can be calculated as the mean of the two speeds: