Ulu, Mustafa, and Kemal Özdemir. “Determining the Mental Estimation Strategies Used by Fourth-Grade Elementary Students in Four Basic Mathematical Operations”. International Electronic Journal of Elementary Education 11, no. 1 (September 29, 2018): 63–75. Accessed December 13, 2024. https://iejee.com/index.php/IEJEE/article/view/548.