Final answer:
The probability that the prefect would be a girl or a boy is 1.
Step-by-step explanation:
In a class of 18 girls and 22 boys, the total number of students is 18 + 22 = 40.
The probability of choosing a boy or a girl as a prefect is the sum of the probabilities of choosing a boy and choosing a girl. The probability of choosing a boy is 22/40 while the probability of choosing a girl is 18/40. Therefore, the probability of choosing a boy or a girl is (22/40) + (18/40) = 40/40 = 1.
So, the probability that the prefect would be a girl or a boy is 1.