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While you were thinking about that question (is the proportion in the bag .6?), I decided to cancel all my appointments, even afternoon tea, and become "scientific".

 

I will put the 20 marbles back in the bag and draw another sample of 20 from the bag, again with my eyes closed.

 

Will the proportion of red marbles be .6 again?

 

It could be. But it probably will not be.

 

I continue to draw samples of n=20. Each time I write down x, the number of red marbles.

 

I also write down p, where p = x/n (the proportion of red marbles in my sample).

 

After a long time, after you have left this session and gone home, I will finally sit down with a cup of coffee, get out some sort of calculator (or Excel, I like Excel), and

 

compute the average of the p values,

 

compute the standard deviation of the p values.

 

Then what do I do?

 

I proceed to the next topic and talk theory stuff.