title: Finding sigma of Gaussian
body: <p>Is there a simple equation which given the area of the shaded part and the mean, gives you the corresponding sigma for a normal distribuion? </p>
  
  <p>P.S the shaded part corresponds to the area under the section of the Gaussian curve which lies on the negative x-axis. In my application this will correspond to the cross over probability.</p>
  
  <p>Thanks
  <a href="https://i.stack.imgur.com/VLhNT.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/VLhNT.jpg" alt="enter image description here"></a></p>