Final answer:
To find the probability that at least one out of 7 devices will function for at least 40 months, use the complement rule. The probability is 1 minus the probability that none of the devices will function for at least 40 months.
Step-by-step explanation:
To find the probability that at least one out of 7 devices will function for at least 40 months, we can use the complement rule. The complement rule states that the probability of an event not happening is equal to 1 minus the probability of the event happening. So, the probability that at least one device will function for at least 40 months is equal to 1 minus the probability that none of the devices will function for at least 40 months.
Let's assume that the probability that a device functions for at least 40 months is p. The probability that a device doesn't function for at least 40 months is then 1 - p. Since the devices are independent, the probability that none of the 7 devices function for at least 40 months is (1 - p)^7.
Therefore, the probability that at least one device will function for at least 40 months is 1 - (1 - p)^7. You are given the probability, you can substitute the value of p and calculate the probability.