This Wikipedia article) says that the total biomass of ants and humans may be more or less equal, although there is considerable uncertainty over the ant biomass. The _population_ of ants is much greater than the human population, but each individual ant obviously has a much smaller mass, by a factor of more than $10$ million.
The purpose of asking this type of question in an examination is to get you to explain your reasoning process when approaching the problem. You are not expected to know the answer - indeed, in this case it seems that no-one knows the actual answer.