Science as inquiry and mathematics as problem solving are conjoined fraternal twins attached by their similarities but with distinct differences. Inquiry and problem solving are promoted in contemporary science and mathematics education reforms as a critical attribute of the nature of disciplines, teaching methods, and learning outcomes involving understandings, attitudes, and processes. The investigative and quantitative processes involved in scientific inquiry include seeking problems, identifying researchable questions, proposing hypotheses, designing fair tests, collecting and interpreting data as evidence for claims, constructing evidence-based arguments, and communicating knowledge claims. Within this empirical context, science and mathematics come together to solve problems with evidence, construct knowledge claims, communicate claims, and persuade others that the claims are valid and useful. This study examined the intersection of inquiry and problem solving and the use of mathematics in 26 extracurricular open science inquiries. The category and the appropriateness of the mathematical procedures revealed these students used measurement, numeracy skills of counting and calculation, and tables and graphs in their science inquiries. It was found that most measurements in the science inquiries were used appropriately, but there is room for improvement with other mathematical procedures that involve higher-level thinking skills, such as analyzing and calculating numerical data and interpreting graphs and tables. The findings imply that mathematics and science are connected in inquiry and should be extended to solve real-life problems and that instruction should emphasize comprehending and interpreting data.