Final answer:
The mean low temperature for the five days is calculated by adding all temperatures together and then dividing by the number of days, resulting in -14 degrees.
Step-by-step explanation:
To determine the mean low temperature over the five days recorded in Rigby, we add all the low temperatures together and then divide by the number of days:
(-12) + (-17) + (-11) + (-12) + (-18) = -70
Now divide -70 by 5 to find the mean:
-70 ÷ 5 = -14
Therefore, the mean low temperature for the five days is -14 degrees, which corresponds to option (a).