#### Answer

a. $0.324$
b. $0.676$
c. $0.999$
d. Events in (a) and (b) are complementary.

#### Work Step by Step

a. What is the probability that all 4 flights are on time?
$p=0.9\times0.8\times0.5\times0.9=0.324$
b. What is the probability that at least 1 flight is not on time?
$p=1-0.324=0.676$
c. What is the probability that at least 1 flight is on time?
First find all are not on time: $p=0.1\times0.2\times0.5\times0.1=0.001$
so the probability that at least 1 flight is on time is $p=1-0.001=0.999$
d. Which events are complementary?
Events in (a) and (b) are complementary.