i've tried searching the net but couldn't find anything useful
An important result: AM>GM>HM unless the numbers are all equal
can someone please explain what is harmonic mean and an example or two?
You may have solved the problems without knowing that you are using HM.
example: Mr X travels 200 miles to city A, 50 miles/hour. On his return, his speed is 40 miles/hr.
What is the average speed?
Answer: HM of 50 and 40.
I havent seen Geometric mean in GMAT. So, I guess HM is out of the question. But it is worth knowing.