First, calculate the probability that a person picked at random did respond. If 90 people did not respond out of a total of 285, then 195 people did respond. So, the probability that a person picked at random did respond is 195/285 0.684. Next, calculate the probability that three people picked at random all responded. Since the events are independent (the response status of one person doesn't affect the response status of another), you can simply cube the probability from step 1: (195/285)^3 0.320. Finally, subtract the probability from step 2 from 1 to find the probability that at least one person did not respond: 1 - 0.320 = 0.680 or 68.0%. paraphrase this