The bacteria in a jar triple every 20 seconds. After three minutes, there are 275,562 bacteria in the jar. How many were in the jar at the beginning of the experiment?
I need to find the initial number of bacteria, which I will call x. I know that the bacteria triple every 20 seconds, so after 20 seconds, there will be 3x bacteria, after another 20 seconds, there will be 3 times 3x, or 9x bacteria, and so on. I can write this as a general formula: after n 20-second intervals, there will be 3^n times x bacteria. Three minutes is 180 seconds, so there are 180/20 = 9 intervals of 20 seconds in three minutes. Therefore, after three minutes, there will be 3^9 times x bacteria. But I also know that after three minutes, there are 275,562 bacteria. So I can write an equation: 3^9 times x equals 275,562. I can simplify this equation by dividing both sides by 3^9, which is 19,683. This means that at the beginning of the experiment, there were 14 bacteria in the jar. 