AbstractIn this dissertation the most common methods of solution, in whichThe Rule of Three is included, are presented. The Rule of Three taskshave been considered in various manners during the centuries. Thisdissertation examines how The Rule of Three, as a rhetorical methodof calculus, is presented in Swedish textbooks from the 17th centurytill the beginning of the 20th century. Moreover, a comparativeanalysis, of The Rule of Three tasks and their solutions, is presented.In addition, a variety of other rules are presented and treated asexamples of rhetorical mathematics. Similar to The Rule of Three,these rules are built on proportionality.The tradition that Björk started in using proportionality was continuedby Celsius, Beckmarck and Forsell and later by Björling andZweigbergk. Zweigbergk’s textbook is excellent from a mathematicalas well as from a pedagogical point-of-view. In Zweigbergks’saccount of Regula de Tri the emphasis is on comprehension andmechanical skills.The results of this thesis show that the textbooks can be divided intothree groups, based on their description of The Rule of Three. Group:1. Include the (textbook) authors who strongly emphasizealgorithms and mechanical arithmetics.2. Include the (textbook) authors who build their descriptions ofThe Rule of Three on the theory of proportion.3. Include the (textbook) authors who solve The Rule of Threeproblems through going back to the unit.