Critical thinking ability is the ability to identify problems, evaluate and develop arguments and solve problems appropriately. Critical thinking must be mastered as a fundamental ability that students must possess. One strategy that can develop students' critical thinking skills is giving problem-solving tasks, such as KSN questions. The KSN questions have more complex problems and a very high difficulty level. This study aimed to measure students' critical thinking in solving the problems of the National Science Competition (KSN) in the field of Mathematics. This research is qualitative descriptive research. The research subjects were three 8th-grade students who were members of the competition team of Public Junior high School 3 Siak Kecil. The data collection technique was in the form of a written test to measure students' critical thinking skills. The results showed that students had good mathematical critical thinking skills. Overall, students can investigate the context of the problem (interpretation), model or formulate mathematical problems (analysis), develop answer concepts by applying appropriate strategies (evaluation), and write conclusions (inference). The results of the data analysis concluded that of the three students who took the test, S-1 had excellent critical thinking skills

Mengetahui kesalahan yang dilakukan siswa dalam mengerjakan soal akan mempermudah guru untuk memperbaiki kesalahan yang dilakukan siswa. Didapati masih banyaknya siswa yang melakukan kesalahan dalam menyelesaikan soal matematika yang salah satunya peneliti temukan di SMPN 39 Pekanbaru. Tujuan penelitian ini adalah  untuk  mengetahui  bagaimana  kemampuan  pemecahan  masalah matematis  siswa. Metode yang digunakan dalam penelitian ini adalah penelitian deskriptif kualitatif.Teknik pengumpulan data yang digunakan adalah teknik tes yang terdiri dari 4 soal uraian. Analisis data yang peneliti gunakan yaitu pengolahan data, penganalisisan data dan penafsiran data. Dari analisis data didapat hasil bahwa kesalahan siswa paling banyak terjadi pada soal KPK di tahap memeriksa kembali yaitu sebesar 85% dan pada soal FPB di tahap menyelesaiakan rencana sebesar 82,65%.