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 distribution
and we want to find
then we can use the
– transform
to find a – value then find the probability for this– value from the tables.
Example:
Find
to two decimal places.
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0.07 |
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0.6 |
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0.2486 |
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To find the probability in our tables corresponding to
we 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 find
so 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.