The graph displays the distribution of the heights of 15-year-old boys in three classrooms.

This question assesses interpretation of a statistical graph and understanding of the mean (average). The mean height represents the weighted average of all data points across the three classrooms. From the plotted distributions, the center of mass of the combined data lies just under 172 cm. Option D, 171.9 cm, most accurately represents the mean height shown by the data. Option A (170.0) is too low, option C (175.0) is too high, and option B (17.0) is clearly incorrect due to unit misinterpretation. On the NEX exam, graph-based questions often test estimation and interpretation rather than exact calculation, especially when raw data values are not individually listed. The correct approach is to identify the overall balance point of the distribution.

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