Question 829059
1.{{{z=(600-500)/80}}}
{{{z=1.25}}}
{{{P(1.25)=.8944}}}
You can calculate  {{{P(-1.25)=0.10565}}} or use symmetry since {{{P(1.25)-P(-1.25)=2*(P(1.25)-P(0))}}}
Either way 
{{{P(1.25)-P(-1.25)=0.7887}}}
2. Using EXCEL's NORM.INV function for {{{P(z)=0.90}}}, then {{{z=602.4}}}