An educational psychologist wishes to know the mean number of words a third grader can read per minute. She wants to ensure that the estimate has an error of at most 0.3 words per minute. A previous study found that the mean was 40.2 words per minute. Assuming that the variance is 15.21, what is the minimum number of third graders that must be included in a sample to construct the 80% confidence interval? Round your answer up to the next integer.