The MaSuD project, an Eramus+ partnership (2020-1-FR01-KA229-079794), combines two educational issues: math anxiety and raising awareness on environmental issues. We believe that learning mathematics through open-ended problems allows students to overcome math anxiety and acquire various concepts and thinking skills. Our objectives: 1. raise students' awareness of environmental issues and sustainable development by having them manipulate mathematical tools that allow them to measure the impact of particular actions; 2. increase students' interest in science by proposing open problems to be dealt with in groups; 3. develop students' math competences, creativity, cognitive abilities, and collaboration skills; 4. practice written and oral English via international collaboration and communication.