Scores on an exam are normally distributed with a mean of 76 and a standard deviation of 10. In a group of 230 tests, how many students score below 66?

about 93 students
about 115 students
about 37 students
about 78 students

Question

Scores on an exam are normally distributed with a mean of 76 and a standard deviation of 10. In a group of 230 tests, how many students score below 66?
 
  
 about  93 students 
 about 115 students 
 about 37 students 
 about 78 students

amistre64 · Answer

how many standard deviations is 66 away from the mean?

amistre64 · Answer

76 + x(sd) = 66

x(sd) = 66 - 76

x = (66-76)/(sd)

amistre64 · Answer

then depending on accuaracy we could possibly use the empirical rule to determine the rest