If `P_0` stands for the starting population (that is, `P_0 = 240text[,]000text[,]000`), then the population at the end of the first year will be `P_0+0.02P_0` or `1.02P_0`. Each year the population will get multiplied again by `1.02`, so at the end of three years the population will be `1.02^3P_0. When we substitute `240text[,]000text[,]000` for `P_0` and multiply by `1.02^3`, our computer or calculator says the new population is `254text[,]689text[,]920`. But the original data had only two significant digits (`2` and `4`), or maybe three — we can't be sure about the first `0` — and we can't possibly know more precise information about population at a later date simply by doing calculations with an abstract model. Thus the best answer to our question is “about `250text[,]000text[,]000`” — an answer with the same number of significant digits as we started with. It would not be wrong to say “about `255text[,]000text[,]000,`” as long as we understand that there is no solid reason to believe the second `5`. It definitely is wrong to report `254text[,]689text[,]920` as the answer, because this implies that you know the population to a high degree of accuracy, and you certainly don't.