In order to neutralize the acid in a waste stream (composed of H2SO4 and H2O), dry ground limestone (composition 95% CaCO3 and 5% inerts) is mixed in. The dried sludge collected from the process is only partly analyzed by firing it in a furnace, which results in only CO2 being driven off. By weight the CO2 represents 10% of the dry sludge. What percent of the pure CaCO3 in the limestone did not react in the neutralization?