When do I substract from 1?

Always sketch the normal curve situation first.

Remember the Standard Normal Distribution tables almost always give the area/probability from left infinity to the z-value in question; check for sketches on the tables you use to confirm. The Excel Norm.xxx functions also return the probability to the left of the z-value in question. If the problem asks for probabilities < x, you use the value directly from the table/function. If it asks for the probability > x, that is when you subtract the table/function value from 1.
less-than-x
greater-than-x

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Scroll to Top