First, students record the current temperatures for the twelve cities. Then, students must put the values in order from least to greatest. Often students do not understand the concept of negative values unless they are put into context. Explaining that a negative number, like -2, is like owing money to the cafeteria. -2 is like owing 2 dollars. -9 is like owing nine dollars. So -9 is less than -2.


Next, students must create a number line to display the data they have collected. They must look at the least and greatest values to determine how to number. Often, students will only number using the values in the data set. It is important that they know that all numbers, in this case from -9 to 11, must be recorded on their number line if they are counting by ones. Otherwise, if they are skip counting by two or five, the intervals must be regular. The students use Xs to record the temperature values on the line plot.


To find the range of data, this student "hopped" from -9 to 11.
Before introducing that 11 - (-9) = 20, students need the opportunity to explore the logic of positive and negative values on a number line. (This student does need to add to her explanation, explaining that she found the range by counting the intervals from the least value, -9, to the greatest value, 11). Students then went on to compare the temperatures of the cold cities by counting the intervals from one city to another on the number line, determining, for example, that Kaktovik (-7º C) is 9º colder than Spirit River (2º C ).

Indicator:
6.5.2.3 compare, order, and describe integers on a number line.