The probability table is attached below
The probability that at least four of the subjects experience headaches.
Probability of at least 4 means x is greater than or equal to 4
Given n= 5 so we find probability (x=4) and (x=5)
P(x>=4) = P(x=4) + P(x=5)
Given P(x=4) is 0.3732
Also P(x=5) is 0.1882
P(x>=4) = P(x=4) + P(x=5)
= 0.3732 + 0.1882 = 0.5614
the probability that at least four of the subjects experience headaches is 0.5614
(b) No, it is not unlikely that the probability fewer than four subjects will experience headaches