The bacteria took 1 hour and 40 minutes to fill the first bottle and it took only 10 minutes to fill 3 more. This is because of the amount of bacteria, for the first bottle there were only a few so it took them time to grow and multiply but once there were a lot the process starts to get faster. Think of it like this if you have 1 bacteria it will multiply into 2 bacteria. The 2 will multiply into 4, then 8, 16, 32, 62, 124 and so on. Do you notice how the numbers are getting bigger every time? Each number is being multiplied by 2 so the growth rate speeds up very quickly, which is why it took the bacteria 1 hour and 40 minutes to fill the first bottle and only 10 minutes to fill the other 3.
The bacteria took more time to double from 1 cell to a bottle full of cells. Once the bottle was full, each cell in the full bottle doubled, causing an additional bottle to be filled in 5 minutes. Then the 2 full bottles doubled in the next 5 minutes, causing all 3 bottles to be full
