I'm having difficulty finding the solution for the following problem:
A hedge fund has 70 employees. For any two employees $X$ and $Y$ there is a language that $X$ speaks but $Y$ does not, and there is a language that $Y$ speaks but $X$ does not. At least how many different languages are spoken by the employees of this hedge fund?
From the given hint, I know there are 70 unique combinations, such that, for any two sets, there is at least one element that is present in one set and not in the other.
From the formula of combination, I have:
$$x C y = 70.$$
I'm stuck at the above point, as there are two unknowns and one equation.