statistics
posted by K.T .
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?

http://davidmlane.com/hyperstat/z_table.html
I get below 50.3 
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? 
Good question; ask your friend. It makes no sense. See the link I posted.
Respond to this Question
Similar Questions

math
For a class of 43 students, for a certain test, the mean grade is 67 and the standard deviation is 7. a) how many students should receive a C? 
math
A class of 43 students took an exam. Their mean grade average is 67 and standard deviation is 7. a) how many students should get a C? 
math
For a class of 43 students fora certain exam, the mean grade is 67 and the standard deviation is 7. a) How many students should receive a C? 
Statistics
In Professor Smith's statistics course, the correlation between students' total scores before the final exam and their final exam scores is r = 0.67. The preexam totals for all students in the course have a mean of 275 and a standard … 
college
Suppose that, for a certain exam, a teacher grades on a curve. It is known that the grades follow a normal distribution with a mean of 70 and a standard deviation of 7. There are 45 students in the class. How many students should receive … 
statistics
In a large class, there were 220 students who wrote both the midterm and the final exam. The standard deviation of the midterm grades was 14, and that of the final exam was 20. The correlation between the grades on the midterm and … 
statistics(business)
Large group of students took a test in English and the final grades have a mean of 75 and a standard deviation of 8. If we can approximate the distribution of these grades by a normal distribution. What percentage of the students (ii) … 
statistics
Large group of students took a test in English and the final grades have a mean of 75 and a standard deviation of 8. If we can approximate the distribution of these grades by a normal distribution. What percentage of the students (ii) … 
Stats
In a large section of a statistics class, the points for the final exam are normally distributed, with a mean of 72 and a standard deviation of 9. Grades are to be assigned according to the following rule: The top 10% receive A's. … 
maths, statistics
Marks in an examination are distributed normally with a mean of 55 and standard deviation of 15. 200 students sit the exam. (a) If the passing mark is 40, what is the number of students expected to fail?