Answer
It is doubtful that there truly is a decrease in the mean score.
Work Step by Step
Since 1975 had the highest mean score, this indicates that there was an increase between 1972 and 1975, after which there appeared to be a decrease
The Basic Practice of Statistics 7th Edition
by Moore, David S.; Notz, William I.; Fligner, Michael A.
Published by
W. H. Freeman
ISBN 10:
146414253X
ISBN 13:
978-1-46414-253-6
Chapter 21 - Comparing Two Means - Chapter 21 Exercises - Page 510: 21.31b
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