Using the arrangements formula and the probability concept, it is found that:
The number of possible arrangements of n elements is given by:
[tex]A_n = n![/tex]
A probability is the number of desired outcomes divided by the number of total outcomes.
In this problem, there are 4 runners, hence, the number of different ways the race can be completed is:
[tex]A_4 = 4! = 24[/tex]
Considering A first and C second, for the third and fourth positions, it is an arrangement of 2 elements, hence:
[tex]A_2 = 2! = 2[/tex]
The probability is:
[tex]p = \frac{2}{24} = \frac{1}{12}[/tex]
[tex]\frac{1}{12}[/tex] probability that A finishes first and C finishes second.
A similar problem is given at https://brainly.com/question/24648661