Jim, thanks for your response. The RandomReal[] should be a random number between 0 and 1, not 1 and 100.
My idea is this:
I have an expression 100*Log[(-1)/(RandomReal[] - 1)]
I want to solve this 100 times, using a random real number between 0 and 1 each time.
Then I will get 100 values of r = 100*Log[(-1)/(RandomReal[] - 1)]
, and then I have to calculate the mean of all of these values.