In this case we don’t know the total colleagues in his office, so if we are interacting with 50 colleagues won’t the probability of the being infected (the given probability = 0.1) change depending on which sample of 50 we have met?

and what if the case that there are 250 colleagues (10% is 25) so in this case we cant assume n to be 50 , as its not possible to meet 50 infected, so will the formula still work on this case?