Missing Test Scores

A student went to a professor's office to make up a test.  The professor graded the exam and computed the mean and standard deviation of all of the test scores.  Unfortunately, he forgot to record the student's grade and lost the test.  Find the missing test score if the standard deviation was 8.596.  The other test scores were:

65,71,72,72,74,74,75,75,75,75,75,78,78,79,79,81,81,81,81,82,83,89, 90,90,92,94,96,98,100

Submit your idea for an investigation to InterMath.