Hi I'm doing a further maths AS level (UK high school qualification) and I'm doing a module on statistics.

My problem lies with mean population hypothesis testing. A normal distribution is assumed, and I'm using the method illustrated in the following example (taken from an answer scheme):

N(355,52^2)

Null Hypothesis: mu=355

Alternative Hypothesis: mu =/= 355 (2-tail test) (=/= is not equal btw :P)

Test statistic= (344-355)/(52/sqrroot(25)) where 344 is the observed value and 25 is the total number of things in the sample I'm testing.

I'm then told to compare the test statistic to the critical value of z (I don't really know what this is)

So in the example the answer says to compare the test statistic to the 5% level 2 tailed critical value of z which equals 1.96.

Now I know this z thing has something to do with the inverse normal tables, but my question is how do you get the critical value of z from the inverse normal tables?

How, in the example, did the value of 1.96 come about?

Thanks!

The inverse normal table I'm talking about

:

page 22 of

http://www.mei.org.uk/files/pdf/formula_book_mf2.pdf