The math problem is that in addition to taxes collected from all casinos by the state, the Chicago casino would have to hand over an additional one-third of adjusted gross receipts, which would be used by Chicago’s City Hall to help shore up its depleted pension funds. If not for this extra privilege tax, as that gouge is politely called, a casino is far more likely to be successful, according to the feasibility study. Under the current law, the study says, the casino would pay an effective tax rate of 72 percent.