This paper provides an exemplar for textbook writers and teachers to design tasks for mathematical literacy and implementing them into classrooms. Mathematical literacy is the kernel focus of the current innovations of 12-year compulsory education. This paper begins by briefly introducing the significance and the meaning of mathematical argumentation. Then, a task design for conjecturing integrated into mathematics content with recognizing various triangles and its properties as an example to illustrate the meaning of transforming intended curriculum into written curriculum. It is suggested that mathematical conjecturing is an approach to evoke mathematical argumentation as one aspect of mathematical literacy. Mathematical conjecturing is an approach for illustrating mathematics as a language and mathematics as scientific pattern. Mathematical conjecturing has a power of construing a series of connected mathematics properties or mathematics concepts as an approach to enhancing mathematical literacy. Moreover, mathematics as a language and mathematics as a pattern of science are achieved via conjecturing. Students convince others via warrants and reject the arguments of others using rebuttals or they support others’ arguments via warrants or backing. This paper concludes with remarks for mathematical textbooks for textbook editors and teachers.