# Normal Distribution, percent less than mean minus one std. dev

GRE Question, part b. My answer is 16%, but the book says 15%. Why?

mean = 65 cm stdev = 5 cm

Probability that penguin chosen at random will be less than 60 cm is 16%, it shows in Normal Distribution graph. Why would the book say it is 15%

### Update

During GRE, we can use standard calculator, i.e no scientific calculator. And I don't believe they will provide standard distribution table.

Kindly explain how to DERIVE the 15%, I wish to understand the mathematics.

• @AhmedS.Attaalla I need to know how they got the answer for the actual GRE exam – Rhonda Jan 2 '16 at 1:31

• A standard distribution table, a statistical calculator, the internet, ... wolframalpha.com/input/?i=one+standard+deviation+from+the+mean – Ian Miller Jan 2 '16 at 2:14