Katherine is very interested in cryogenics (the science of very low temperatures). with the of her science teacher she is doing an experiment on the affect of low temperates on bacteria. she cools one sample of bacteria to a temperature of -51 c and another to -71 c. what was the temperature difference in the two experiments?

The change from the first experiment to the second one is

                     (second temperature) - (first temperature)

                 =                 (-71°C)          -              (-51°C)

                 =                                  - 20°C .

The temperature in the second experiment is  20°C  lower
than the temperature in the first one.