Hatem , A. . ., and K. . . Ebraheem. “Effectiveness of Universal Concept of Mental Arithmetic System (UCMAS) In The Developing Of Visual Thinking Among Fourth Grade Students (Quasi- Experimental Study In Private Schools At Lattakia)”. Tishreen University Journal- Arts and Humanities Sciences Series, vol. 38, no. 1, Jan. 2017, https://journal.tishreen.edu.sy/index.php/humlitr/article/view/2318.