For the antibiotic to be sufficiently effective, it has to kill at least 90% of bacteria when applied to a harmful bacteria culture. She applied her antibiotic to a Petri dish full of harmful bacteria, waited for it to take effect, and then tried to estimate the percentage of dead bacteria in it. She took a random sample of 300 bacteria and found that 94% of them were dead. Then she calculated the margin of error and found that the true percentage of dead bacteria is most likely to be above 90%. So what's happening over here, she's trying to figure out what percentage of the total population of bacteria died. And maybe there's something about this bacteria, maybe just when you look at it from the naked eye, you can't tell whether the bacteria died or not. And so she decides to estimate the true percentage by sampling 300 individual bacterium, or I always forget the singular case, by sampling 300 bacteria.