at least one lightbulb fails, then the string of lightbulb will fail.
so we shuold rule out the probability that no lightbulb fails. for
each individual lightbulb the probability of failing during
time period T is 0.06, so, the probability of unfailing is (1-0.06), and the probability of unfailing for 10 lightbulbs is (1-0.06)^10, then the probability of failing for at least one lightbulb is 1-(1-0.06)^10.