Suppose the proportion of men to women in a class is 1:4 (the number if people does not matter now). In other words, 4:1 equals to the proportion of women to men.

It means if you randomly divide the people in the class into groups of five and you pick out a single group, the most likely distribution of sexes would be one male individual against four female individuals.

Now let me express the situation in terms of percentage. You will have to draw your conclusions.

Suppose the percentage of men in a class of mixed sexes is 20%. In other words, women comprise 80% of the class. Now, if you randomly divide the class into groups of five, it won't on average affect the percentage. Right? This means if I pick out a single group of five people, the most likely distribution of sexes would be one he and four she. Same as with the proportional example. Why?

80% = 4*(20%)

20% = 1*(20%)

4:1 appears here too.

Yes, it is.