Help! IB Maths HL OPtion Statistics

[iamnotsam]

Textbook from Haese & Harris (Mathematics for the International Student – Mathematics HL (Options)

On page 80 are 2 examples; in Example 43 Z is used as test-statistic, and in Example 44 the test statistic t is used.  Why not Z in both cases, because  variance [sigma square] is given – or am I now confused??  I is said on page 77 that you use Z when  is known, and t when  variance is unknown.  Please help?!

[astarmathsandphysics]

Textbook from Haese & Harris (Mathematics for the International Student – Mathematics HL (Options)

On page 80 are 2 examples; in Example 43 Z is used as test-statistic, and in Example 44 the test statistic t is used.  Why not Z in both cases, because  variance [sigma square] is given – or am I now confused??  I is said on page 77 that you use Z when  is known, and t when  variance is unknown.  Please help?!

If the variance is given use z, if variance is not given use t so that is ok.

[iamnotsam]

Yes, I agree with that; but in both of these case variance (st dev.) had been given....  So why not Z in both cases?

[milton]

Maybe the sample variance is given as opposed to the population?

The examples COULD be wrong, in fact my classmates get to 'beta-test' the new big blue IB Maths Higher book, we came to the conclusion that it was a pile of sh*t with 50% of the answers completely wrong and 10% of the examples screwed up. Though our report came in too late for the school to cancel their orders, so the younger years are stuck with them xD.

And yes, we went through the IB using A-level text books.

[S]

I'm actually pretty interested in seeing that options book, could you maybe throw it on freeetextbooks.com? Or is there no PDF for that one?