Final answer:
The temperatures from least to greatest are arranged as: 0.5°C, 0.8°C, 0.9°C, 1.20°C, and 2.0°C, with 0.5°C being the lowest and 2.0°C being the highest of the recorded temperatures.
Step-by-step explanation:
The student has asked to organize the recorded low temperatures in degrees Celsius from least to greatest, with the least number at the bottom. The numbers given are: 0.9°C, 0.8°C, 1.20°C, 0.5°C, and 2.0°C. We will arrange these temperatures in ascending order. So, the temperatures in order from least to greatest are 0.5°C, 0.8°C, 0.9°C, 1.20°C, and 2.0°C. This ordering reflects the increasing values of the recorded low temperatures over the last week, with 0.5°C being the lowest and 2.0°C being the highest.