There are 10 female students and 20 male students. If we were to divide each number by 10, we would get 1 and 2, respectively. That means for every 1 female student, there are 2 male students. The ratio would then be 1:2.
What is the highest common factor of 12 and 32? It is 4, so we divide both numbers by 4. This gives us 3 : 8. This cannot be simplified further, therefore it is the simplest form.