4.1 is a measure to the nearest tenth.
The value preceding it is 4.0 while the value following it is 4.2
The midvalue of 4.0 and 4.1 is 4.05 while the midvalue of 4.1 and 4.2 is 4.15
Therefore, the class interval of a measurement values reported as 4.1 cm is 4.05 to 4.14 cm