Question

Can someone give me a refresher on standard deviation?

A normal distribution has a mean of 700 and a standard deviation of 25. What is the probability
that a value selected is at most 650?

Answer 1

a) 0.0235
b) 0.700
c) 0.025
d) 0.975

Answer 2

Using the 68-95-99.7 Rule (sort of):
650 would be two standard deviations from the mean. The "at most" part is important! It means that you only include the left tale ( so from far left to 2nd sd - take a look at the attached image)
you add:
0.15% + 2.35% = 2.5% = .025