About the standard nonnormal distribution's 'n' size

The book says, if the ‘n’ size is large enough, we can normally standardize nonnormal distribution.

I had known that the large means ‘n≥30’, but the book have not used the z-distributin.

Why I ask this question is the Kaplan 2015 lv1 note 297p’s example uses not z-distributin but t-distribution.

How much is enough?

The t-distribution is more conservative, but when n ≥ 30, the z-distribution is acceptable.

On the exam, you’ll use whichever distribution they give you.

s2000) Thank you for answering.~

My pleasure.

Same problem with the size of the sample

in B. the sample size is 40 which is greather than 30, and the t-statistic should be applied here according to the table below, am i right ?

I suspect that you’re missing the point of the question.

You would use a t-statistic if you had data about the earnings themselves. But here _ you don’t _ have data about the earnings themselves, you have data about analysts’ estimates of the earnings. The point is that you cannot create a confidence interval for some data when all you have is a bunch of guesses on those data (even if they’re educated guesses).

it’s all clear now

thank you

Good to hear.

My pleasure.