Normal Standard Distribution problem

Question

Use the table of areas under the standard normal curve to find the probability that a z-score from the standard normal distribution will lie within the interval. (Round your answer to four decimal places.)

a) z < 2.5

Answer 1

Your table gives you the percentage under the normal curve that is to the left of your given Z-Score up to the mean. So if given a problem that involves < and z is positive, the problem is fairly easy. Simply use your table to find the desired probability/portion, then add 0.5 (the other half of the normal curve).

If you come across other problems that involve > with a positive z, your would have to follow the same procedure as above, then subtract it from 1.

If your z-score is negative and symbol is <, you can use the positive value in your table and subtract it from 0.5 to find your probability.

If your z-score is negative and your symbol is >, you can use the positive value in your table, then add 0.5

Ranges are the only other kind of problem you may see. If the ask you to find a probability between two z-scores, use the table to find each individual probability, then take their difference.

Hope this helps!