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= (X-64)/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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