New percetage = .98
198 - x / 200 = .98
x = 2
x number of men to leave the group
If 2 men leave the group then why are you still dividing by 200? For that to be true wouldn't 2 women have to join the group? If 2 men left it would be 196/198, which is not 98%. You have to take into account that any man that leaves also decreases the total. The total is the number of men (198)+ women(2). Therefore if you decease the number of men from numerator, you have to also decrease it from the deominator.