I am currently reading Investing in the Unknowns and Unknowable by Richard Zeekhauser.
On page 6, 3rd paragraph, there is following lines:
Thus, if a price 100 goes up or down by an average of 3 each year or up by a ratio of 103/100 or down by 100/103 hardly matters. But change that 3 to a 50 and the percentage symmetry helps a great deal. The price becomes 100(150/100) or 100(100/150), which has an average of 117.
I am not able to work out how he got 117.