To determine the number of bacteria at 8:00 a.m., we need to work backwards from the known amount at 9:00 a.m., which is 120 bacteria. Since the bacteria double every hour, we can represent the number of bacteria at 8:00 a.m. using the following relationship:
At 9:00 a.m., there are 120 bacteria, which means that at 8:00 a.m., the number of bacteria was half of that:
\[ n = \frac{120}{2} \] \[ n = 60 \]
Now, we want to write an equation that represents this relationship (the number of bacteria at 8:00 a.m. in relation to the 9:00 a.m. count):
If \( n \) is the number of bacteria at 8:00 a.m., then:
\[ 2n = 120 \]
This means that the equation 2n = 120 correctly models the relationship.
The correct response is: 2n = 120; at 8:00 a.m., there were 60 bacteria.