On the same day at school, 3/10 of the students were wearing skirts and 1/4 of the students were wearing pants. what fraction of the students were wearing shorts?

thats not a system of equations, that is a solution

there is only one way to arrange all the eight relative to each other because they are not distinct. we have

now there are nine places to place an (and not more than one in one place).   because we have four symbols, we need to choose four of these nine places to insert an . order does not matter because the are not distinct.

thus there are 1 · c(9,4) ways, or, if we calculate it,

thus there are 126 ways to form such "words."