A test with normally distributed results was returned to a class of 100 students. Later, the teacher realized an error was made and added 10 points to each student's score. Which of the following must have changed as a result of the increase in scores?

If each student's score is changed by the same amount, the spread (variance, standard deviation) will not change. A student's percentile would also remain the same. The mode will increase by 10 regardless of what the initial mode was.