Xiaoming may be in People's or Tsinghua, Xiaohong may be in Peking University or People's, and because he studies physics in Tsinghua, he doesn't study mathematics in Peking University, Xiaohong doesn't study chemistry, and Xiaohong studies mathematics in People's. From the above analysis, we can see that Xiaoming studies physics in Tsinghua University and Xiao Qiang studies chemistry in Peking University. To sum up: Xiaohong is in the Department of Mathematics of Renmin University, Xiaoming is in the Department of Physics of Tsinghua University, and Xiao Qiang is in the Department of Chemistry of Peking University.