This is a short 10-slide PowerPoint presentation that shows how to convert a number line with positive numbers into a number line that includes both positive & negative numbers. It also describes opposites as well. Symmetry is described and used to extend the number line. You would probably spend about 15-20 minutes of class time to cover the content in this presentation. The content is based on Common Core standard CCSS.Math.Content.6.NS.C.6a under the domain Number System. Use the presentation for a full class or for individuals needing more help or may have missed the lesson.