Find the area between x = 9.5 and x = 23 under a normal distribution curve with μ = 20 and σ = 4 .

Answer 1

use my favourite stats webpage
http://davidmlane.com/hyperstat/z_table.html

make sure you click "area from a value"
enter 20 as the mean
4 as the sd
click on "between" and enter 9.5 and 23

calculate to get 0.769