The principal of Paul Revere High School bragged that his 2016 graduating class of 1500 students achieved impressive scores on their ACT exams. He announced that an “astounding” 36% of the class got a score of 29 or higher, 54% got a score of 21 to 28, and only 10% less than 21. You want to test whether these ACT results are really that astounding. You visit the ACT website to see that the national results are 34% getting a score over 28, 58% getting 21 to 28, and 8% less than 21. Test whether or not the principal is correct to brag that his proportions were more impressive than the national performance. Use an alpha of 0.05.   So I kinda understand the question. I am mostly confused about how to determine the degree of freedom to get the critical value. Like I know the formula is d-C, and C is the number of categories in the word problem, but is there 3? Or am I just totally wrong?

Glencoe Algebra 1, Student Edition, 9780079039897, 0079039898, 2018
18th Edition
ISBN:9780079039897
Author:Carter
Publisher:Carter
Chapter10: Statistics
Section10.6: Summarizing Categorical Data
Problem 11CYU
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The principal of Paul Revere High School bragged that his 2016 graduating class of 1500 students achieved impressive scores on their ACT exams. He announced that an “astounding” 36% of the class got a score of 29 or higher, 54% got a score of 21 to 28, and only 10% less than 21. You want to test whether these ACT results are really that astounding. You visit the ACT website to see that the national results are 34% getting a score over 28, 58% getting 21 to 28, and 8% less than 21. Test whether or not the principal is correct to brag that his proportions were more impressive than the national performance. Use an alpha of 0.05.
 
So I kinda understand the question. I am mostly confused about how to determine the degree of freedom to get the critical value. Like I know the formula is d-C, and C is the number of categories in the word problem, but is there 3? Or am I just totally wrong? 
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