Inverse standard normal CDF We are dealing with a standard normal random variable. We have $$\Phi(c) = 0.8$$ where $c$ is just some arbitrary number and $\Phi$ is just the usual notation for the CDF of a standard normal distribution. 
I want to find such a $c$ so that this equation holds, i.e.: $$c = \Phi^{-1}(0.8)$$
where we just take the inverse function. How do I find this on a z-table?

It depends, if you have a table that gives "area to the left", then 
look up the row that has area = .8. The standardized score $c$ should be $0.8416212$. 
Some tables are defined as area in the middle, then that's a little trickier.
