Class boundaries need to be defined so that a point on the boundary is unambiguously placed in one class or the other. With these boundaries, a value of 120 might be placed in the first or the second class—we don't know which.
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It is customary to define class boundaries between data values 60.5–120.5, for example, so that no data value can fall on the boundary, or as a semi-open interval [60, 120), so that a boundary value is clearly placed into a specific class.
