i know that two tailed z values for 90% sig = 1.65 95% 1.96 99% 2.58 are we going to have to know the z values for one-tailed tests are 90% 1.28 95% 1.65 99% 2.33 ?

I find it easier (?) like this: Link it to the probability itself: 1% implies 0.99 (for 1 tail) or 0.995 (for 2 tails) 5% implies 0.95 (for 1 tail) or 0.975 (for 2 tails) 10% implies 0.90 (for 1 tail) or 0.95 (for 2 tails) Then you just ask which probability it is. If it is 0.995 ==> 2.575 If it is 0.990 ==> 2.325 If it is 0.975 ==> 1.96 If it is 0.95 ==> 1.645 If it is 0.90 ==> 1.285

beautiful. thanks