# For a bell curve with mean 7 and standard deviation 3, how much area is under the curve, above the horizontal axis, and between x = 2.5 and x = 11.5?

your normalized standard deviation is 1,5 because $\sigma = \frac{7 - 2.5}{3} = 1.5$ and also $\sigma = \frac{11.5 - 7}{3} = 1.5$.