The Minnesota School Mathematics and Science Teaching (MINNEMAST) Project is characterized by its emphasis on the coordination of mathematics and science in the elementary school curriculum. Units are planned to provide children with activities in which they learn various concepts from both subject areas. Each subject is used to support and reinforce the other where appropriate, with common techniques and concepts being sought and exploited. Content is presented in story fashion. The stories serve to introduce concepts and lead to activities. Imbedded in the pictures that accompany the stories are examples of the concepts presented. This unit introduces fractions by comparing different scales on number lines. The concept is built as a ratio between scales. As in the earlier units, operations with fractions are presented through activities involving the number line; the four operations, addition, subtraction, multiplication and division of fractions, are covered in this unit. Worksheets and commentaries to the teacher are provided and additional activities are suggested. (JP)