@article{rathgeb-schnierer_green_2019,  title={Developing Flexibility in Mental Calculation},  volume={44},  ISSN={2175-6236},  url={https://doi.org/10.1590/2175-623687078},  DOI={10.1590/2175-623687078},  number={2},  journal={Educação & Realidade},  publisher={Universidade Federal do Rio Grande do Sul - Faculdade de Educação},  author={Rathgeb-Schnierer, Elisabeth and Green, Michael G},  year={2019},  pages={e87078} }