Flexible equation solving (JYR) is a material package of about 10 lessons for starting equation solving in middle school. The material can be used by teachers, students and, for example, textbook authors. In flexible equation solving, the emphasis is on concepts, thinking out loud, using different solution methods and learning from mistakes. The goal is to increase understanding, flexibility and study motivation. The student and teacher materials are available in Finnish and the student material in Swedish. Flexible equation solving was a development project in the LUMA SUOMI program. JYR was implemented at the University of Oulu Department of Mathematical Sciences in 2014-2019. The project was financed by the Ministry of Education and Culture.