How do I find probabilities using a normal distribution?

It is likely that your calculator has a function that can find normal probabilities, if so it is a good idea to learn to use it so that you can check your probabilities

• • However you?must?show your calculations to get the z values and use the tables to get all the marks

How do I calculate the probability for a normal distribution?

Given the value of P(X < a) ?or P(X > a) ?how do I find the value of?a?

• Given a probability you will have to look through the table of the normal distribution to locate the?z-value that corresponds with that probability
• Look at whether your probability is?greater or less than 0.5?and the?direction of the inequality?to determine whether your?z-value will be positive or negative
  • You do not need to remember these, a sketch will help you see it
• • Always sketch a diagram

• If your probability is less than 0.5 you will need to?subtract it from one?to find the corresponding?z?value
  • Remember that the?position?of the z-value will not change, only the direction of the inequality
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