A culture of a certain bacteria doubles every hour. At 9:00 a.m, there were already 120 bacteria. Which equation represents the number of bacteria, n, at 8:00 a.m? How many bacteria were there?
Options:
n/2 = 120; at 8:00 a.m, there were 240 bacteria
2n = 120; at 8:00 a.m there were 240 bacteria
2n = 120; at 8:00 am there were 60 bacteria
n/2 = 120; at 8:00 am there were 60 bacteria
The correct equation and answer are:
n/2 = 120; at 8:00 a.m, there were 60 bacteria
The reason for this is that the culture doubles every hour. Therefore, at 9:00 a.m there were 120 bacteria, which means that at 10:00 a.m there would be twice as many, 240 bacteria. Since we want to find the number of bacteria at 8:00 a.m, which is one hour before 9:00 a.m, we need to go backward in time. Going one hour backward, from 9:00 a.m to 8:00 a.m, the number of bacteria would be half of what it was at 9:00 a.m. Therefore, the equation is n/2 = 120. To solve for n, we multiply both sides of the equation by 2, giving us n = 240. Thus, at 8:00 a.m there were 240 bacteria.