Posted by K.T on Sunday, January 3, 2010 at 4:11pm.
the average of final exam is 64, the standard deviation is 7. If the teacher set a rule that 1/4 of students who receive the poor grades should stay after class. lower than what mark should the students stay in school?
does anyone know how to solve this?

statistics  bobpursley, Sunday, January 3, 2010 at 4:52pm
http://davidmlane.com/hyperstat/z_table.html
I get below 50.3

statistics  K.T, Sunday, January 3, 2010 at 4:57pm
my friend came out with the following solution.
P(Z<0.675)=0.25
0.675= (X64)/7
but i'm kinda confused.
where did the 0.675 come from?

statistics  bobpursley, Sunday, January 3, 2010 at 8:39pm
Good question; ask your friend. It makes no sense. See the link I posted.
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