To find the number of bacteria at 8:00 a.m., we need to consider that the bacteria double every hour.
At 9:00 a.m. there are 120 bacteria. Therefore, 1 hour earlier, at 8:00 a.m., there must have been half that amount.
To express this mathematically, if \( n \) represents the number of bacteria at 8:00 a.m., we can write the equation:
\[ 2n = 120 \]
This means that at 8:00 a.m. there were:
\[ n = \frac{120}{2} = 60 \]
The correct representation is:
2n = 120; at 8:00 a.m., there were 60 bacteria.