Students also use two-color counters to model and begin to make sense of positive and negative integers. In this system, a positive 1 is represented by one color and a negative 1 by the other. Students determine the value of a pile of counters by pairing up counters, one of each color, setting aside all pairs, and counting the remaining counters. Students read Shel Silverstein's poem A Giraffe and a Half and discuss how to describe an amount that is more than one whole but less than two. Students read The Phantom Tollbooth and discuss the relationships between decimals and fractions in the book.
Students construct a time line to scale to show the history of the earth.
Significant periods and events are shown along the line with numbers reflecting the number of years since the earth's beginning. Develop number sense necessary for estimation. Students imagine collecting a million of something. Then they gather the data they need to make more informed estimates. Students determine the number of decimal places in a simple decimal multiplication product, not by mechanically adding the number of places in the factors, but by estimating a reasonable range for the product and placing the decimal point so that their computed product falls within that range.