3 randomly selected observations form the standard normal distribution are selected. What is the probability that their sum is less than 2?
The Attempt at a Solution
I know that the answer is 0.874928, but I don't know how to get that.
In my mind, you would say that 2/3=0.67, so what is the probability that the average of the 3 values is less than 0.67?
This gets me the wrong answer however.