This formula allows you to calculate a z-score for any data point in your sample. In this case we can work backwards or 100 - 83 or 17 to find the area beyond that point. You would just plug in the Z-score and mean into our formula and then solve for the standard deviation using algebra.
A z score of 0 means 50 of scores fall below the mean score.
Z equals start fraction x minus mu divided by sigma end fraction. In the formula X represents the figure you want to examine. Then I combine the attributes together of one observation using a weighted average. Z x m s.