a) What is the difference between a normal distribution and a standard normal distribution? A normal distribution is the way that scores tend to distribute themselves around a mean. Many variables tend to form a rough bell curve surrounding their mean and tapering to the ends based on the standard deviation. A standardized normal distribution is the distribution you get when you transform the values of a variable in question to a standardized score such as a z score.
b) What is the purpose of using a standard normal distribution instead of the normal distribution?
If you want to look up a given value in a normal distribution to see what area