Solver tool for excel and weighting strategy

Hello, I have two questions: A) I am going through the metrum institute videos about population PK PD analysis. In Lab 2 ( https://www.youtube.com/watch?v=ZA_MpMTFsUs&index=3&list=PLvLDbH2lpyXOETHzGfPGOtXayHNmXT9Cx&spfreload=1), the instructor uses a tool called solver to perform iterations to determine the least objective function value. The instructor is using a Mac (open office). How can I get that tool or add-in in excel? B) In the weighted least square example discussed in the video, the weighting used is (1/observed concentration). What are the other common weighting strategies? Is there any specific reason to prefer one weighting strategy over the other? Thank you, Manu -- *With regards-* *Manushree Bharadwaj, BVSc, PhD Candidate* *Graduate Teaching Assistant* *Department of Physiological Sciences* *Center for Veterinary Health Sciences* *Oklahoma State University* *Stillwater, OK-74074*