Answer: .9424 (94%)
Explanation:
Since the population is large, we can assume each of the four people independently has a 51% (.51) chance of being vaccinated, which means that each of them has a .49 chance of being unvaccinated. The probability that all four of them are unvaccinated is (.49)4 ≈ .0576. Thus the probability that at least one of them has been vaccinated is approximately 1 - .0576 = .9424 or about 94%.