Answer:
There are nine female students, and twenty-two male students.
Step-by-step explanation:
We're told that the total number of male and female students is 31:
[tex]m + f = 31[/tex]
We're also told that there are 13 more male than female students:
[tex]m = f + 13[/tex]
So we can substitute the latter piece of information into the former, which will tell us how many female students there are:
[tex]m + f = 31\\(f + 13) + f = 31\\f + f = 31 - 13\\2f = 18\\f = 9[/tex]
So there are nine female students. We can now take either of the initial tow equations, and plug the resulting f value to find m:
[tex]m = f + 31\\m + 9 = 31\\m = 31 - 9\\m = 22[/tex]
So there are nine female students, and twenty-two male students.