This Instructional Activity is a part of the Lesson 6, Unit 7, Grade 8. In this lesson, students show that a real number possessing a finite decimal expansion is a fraction with a denominator 103.) And, conversely, every fraction with a denominator that is a power of 10 has a finite decimal expansion. Students prove that those real numbers with a finite decimal expansion are precisely the fractions that can be written with a denominator that is a power of 10.