Conceptual understanding is an essential mathematical competence that influences students' success in solving word problems. However, many students still encounter difficulties at different stages of the problem-solving process. This study aims to describe the profile of students’ conceptual understanding in solving arithmetic sequence story problems as assessed by mathematical ability based on Newman’s stages. This study employs a descriptive research design with a qualitative approach. The research subjects consisted of three 10th-grade students from Class XA at St. Arnoldus Janssen High School in Kupang, representing high, moderate, and low levels of mathematical ability. The research instruments used were the Problem-Solving Test (PST) and interviews. Data validity was ensured through time triangulation using PPT I and PPT II. The results showed that subjects with high mathematical ability were able to meet the reading and comprehension stages but still made errors in the transformation stage. Subjects with moderate ability were able to meet the reading and comprehension stages but still made errors in formula application, which affected the problem-solving process and final answers. Meanwhile, subjects with low mathematical ability were able to complete the reading and comprehension stages but made errors in the transformation stage, process skills, and writing the final answer. Thus, students’ conceptual understanding profiles differed across each level of mathematical ability in solving arithmetic sequence word problems. ABSTRAK Pemahaman konsep matematis merupakan salah satu kompetensi yang berperan penting dalam keberhasilan siswa menyelesaikan soal cerita, namun masih banyak siswa mengalami kesulitan pada setiap tahapan penyelesaian masalah. Penelitian ini bertujuan untuk mendeskripsikan profil pemahaman konsep siswa dalam menyelesaikan soal cerita barisan aritmetika ditinjau dari kemampuan matematis berdasarkan tahapan Newman. Penelitian ini menggunakan jenis penelitian deskriptif dengan pendekatan kualitatif. Subjek penelitian terdiri atas tiga siswa kelas XA SMA St. Arnoldus Janssen Kupang yang mewakili kemampuan matematis tinggi, sedang, dan rendah. Instrumen penelitian yang digunakan yaitu Tes Pemecahan Masalah (TPM) dan wawancara. Keabsahan data dilakukan melalui triangulasi waktu menggunakan TPM I dan TPM II. Hasil penelitian menunjukkan bahwa subjek berkemampuan matematis tinggi mampu memenuhi tahap membaca dan memahami, tetapi masih mengalami kesalahan pada tahap transformasi. Subjek berkemampuan sedang mampu memenuhi tahap membaca dan memahami, namun masih mengalami kesalahan dalam penggunaan rumus yang memengaruhi proses penyelesaian dan jawaban akhir. Sementara itu, subjek berkemampuan rendah mampu memenuhi tahap membaca dan memahami, tetapi mengalami kesalahan pada tahap transformasi, keterampilan proses, dan penulisan jawaban akhir. Dengan demikian, profil pemahaman konsep siswa berbeda pada setiap tingkat kemampuan matematis dalam menyelesaikan soal cerita barisan aritmetika.
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