Aritonang, A.R., Minarni, A. and Rajagukguk, W. 2018. Analysis of Differences in Improvement of Mathematical Problem Solving Ability of The Students at Upper Secondary School 3 Sidikalang Based on Contextual Learning Model And Direct Learning Models. Advances in Social Sciences Research Journal. 5, 9 (Oct. 2018). DOI:https://doi.org/10.14738/assrj.59.5226.