To find the number of bacteria at 8:00 a.m., we recognize that the bacteria double every hour. Therefore, if we know the number of bacteria at 9:00 a.m. (120 bacteria), we can find the number at 8:00 a.m. by halving that amount.
- The number of bacteria at 9:00 a.m. is 120.
- The number of bacteria at 8:00 a.m. can be calculated as: \[ \text{Number of bacteria at 8:00 a.m.} = \frac{120}{2} = 60 \]
Now, regarding the equation that represents the number of bacteria \( n \) at 8:00 a.m., since we are halving the number from 9:00 a.m. to get to 8:00 a.m., we can express it as: \[ 2n = 120 \] which means \( n \) (the number of bacteria at 8:00 a.m.) would be 60 when solved.
Therefore, the correct response is: 2n = 120; at 8:00 a.m., there were 60 bacteria.