I flew my tiny seaplane to visit my mother. On the flight up, I flew at 110 mph. On the way home, I flew 90 mph. What was my average speed for the trip?  Options.
A) 198 mph  B) 110 mph  C) 88 mph  D) 100 mph  E) 99 mph

Rationale: ( 110 mph + 90 mph ) / 2 = 100 mph correct answer is : d
Answer: D