Finding standard deviation

Question

How do I calculate the standard deviation when given the mean and percent of area that lies to left of a given value?  

Specifically mean=10.8 and 15% of area lies to the left of 9.3.  What is the standard deviation?

Answer 1

Tabitha,

               From a Normal table the 15% point corresponds to Z=-1.0364. So Z= (9.3-10.8)/sd=-1.0364, solving for sd gives sd=1.44.

 

Jim