A long number line with endpoints of 20 and 75, for example, is drawn on the board where all of the intermediary points are labeled above the line. The labels are then covered by a long piece of paper that can be lifted to reveal them. A student places a finger somewhere on the line and others must estimate the numerical label of the point chosen. The paper is then lifted to check the accuracy of their responses. Explore real-life settings which give rise to negative numbers.
Temperature reports, possibly in both scales, become a part of the everyday calendar routine.
References Baratta-Lorton, Mary. Mathematics Their Way . Eating Fractions . National Council of Teachers of Mathematics. Curriculum and Evaluation Standards for School Mathematics .