Problem of the Month

for March 2010
Prius Problem #2

In our first trip from Fort Collins to Estes Park in our Pius,
we averaged 47.8 mpg on the way up, but 92.2 mpg on the way home
(there is an elevation difference of more than 3,000 feet between Fort Collins and Estes Park).
What was our average miles per gallon over the whole trip if the distances up and back were the same?