The value of serum sodium in a healthy adult population in Maseru is approximately normally distributed with mean 400 meq /L and standard deviation of 20 meq /L.

What is the probability that a healthy adult will have a serum sodium value between 120 and 150 meq/L?

What is the approximate range within which 95% of the healthy population lies?

What serum sodium level is necessary to put someone in the bottom 12.1% of the distribution