Facebook reports that the average number of Facebook friends worldwide is 150 with a standard deviation of 90. If you were to take a sample of 25 students, what is the probability that the mean number Facebook friends in the sample will be 165 friends or more?
Try z-scores. In this case, use the following:
z = (x - mean)/(sd/√n)
With your data:
z = (165 - 150)/(90/√25)
I'll let you finish the calculation.
Next, check a z-table for the probability. Remember the question says "165 friends or more" when you are determining the probability from the table.
I hope this will help get you started.