Calculations Involving The Normal Distribution - Finding Probabilities

If you look at the tables for the normal distribution, along the top and left borders there are z – values. If we have a Normal distributionand we want to findthen we can use the – transformto find a – value then find the probability for this– value from the tables.

Example:Find

to two decimal places.




0.07







0.6



0.2486



To find the probability in our tables corresponding towe go down to 0.6 then along to where there is a 0.07 in top row, reading 0.2486 from the table. This is not the answer yet though.

We have just found the blue area above. We have to add to it the unshaded area to the left, which is 0.5, obtaining 0.7486, because the question was to findso we need the whole area to the left. This is a consequence of our particular normal tables. Not all normal tables will require you to do this.

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