Final answer:
The least count of a ruler with tenths of a centimeter (millimeters) is one millimeter (0.1 cm), enabling measurements with a certain degree of precision in tenths place, while the measurement in hundredths place remains an estimate. A ruler without millimeter markings only provides certainty to the nearest centimeter, making the tenths digit uncertain and less precise for measuring.
Step-by-step explanation:
The least count of a ruler is the smallest measurement unit that it can accurately represent. In the case of a ruler that contains marks for tenths of a centimeter (millimeters), the least count is one millimeter (0.1 cm). This means that we can be certain of measurements to the nearest millimeter. When an object is measured with such a ruler, even though the measurement might be reported as 2.55 cm, there is still an uncertainty in the hundredths place (2.54 cm to 2.56 cm), which reveals that only the tenths place (the 5 in 2.5X cm) can be considered accurate. On the other hand, a ruler without millimeter markings can only measure accurately to the nearest centimeter, and the tenths digit is estimated. Therefore, an object could be measured as 2.5 cm, but the actual length could be anywhere from 2.4 cm to 2.6 cm.