Suciati, Suciati and Puspita, Puspita and Azizi, Azizi USING VARIATION TECHNIQUES OF CONCEPT CORRELATION IN THE PROBLEM BASED LEARNING MODEL TOWARD STUDENTS’ ACHIEVEMENT. Proceeding of International Conference On Research, Implementation And Education Of Mathematics And Sciences 2015 (ICRIEMS 2015), Yogyakarta State University, 17-19 May 2015. ISSN 978-979-96880-8-8