given a normal distribution, does altering the number of subjects change the probabilty of a certain result?

For example, given a normal distribution, the average electric bill is $90, with a standard deviation of $24. I want to calculate probability of a random customer having a bill less than 100. I calculate that at approximately 0.6615 using statcrunch. Now if 50 customers were randomly selected, what is the likelihood that the average bill for this group would be below $100? Is the probability the same?