Suppose that an instructor gives an exam This instructor set

Suppose that an instructor gives an exam. This instructor sets to give those students in the bottom 9% a F on this exam. What will the cutoff be for a 0 or better, if the average score on this exam is 78, with a standard deviation of 8?

Solution

so, bottom 9% score for this class = [ mean - ( z for 91%conf. interval)*(s.d) ]
   = [ 78 - ( 1.340755 * 8 ) ] = 67.27396...
so, you have to get more than 67.27396 to get a grade D or better!...

next no. in the options after 67 is 69!

so, cutoff = 69...