# Number Lines As you have seen in the homework lately, we have been working a lot with number lines in class.  Probably the most challenging form of the number line the students have encountered is the open number line.  This number line has the students make use of their number sense and their spacial sense.  For example, the number line may have a 0 on the left and a 20 on the right.  A blank card is put half-way between the two.  The students then need to think about what number would be half-way between 0 and 20.  While we know that would be 10, it can be challenging for students delving into this study for the first time.

We have also been using the number line to add and subtract in two different ways.  One way is when the number line is going from 0 to 10 by ones.  The thing we are working on here is showing the different jumps.  For example, if the problem is 5+2, we would then either make 5 small jumps to 5 or one big jump to 5.  After that we would take two jumps from there to find the answer is 7.  For subtraction, we start at the highest number and jump backwards from there.  This helps the students to better visualize what is happening when they add or subtract.

The second way we use the number line to add and subtract is when the number line is going from 0 to 100 by 10s.  We do the jumps in the same way for both addition and subtraction.  This has started the student realizing that when they add multiples of 10 to other multiples of 10…the addition is very similar to when they are adding any of the numbers from 0 to 10.  For example, they have been seeing that 50 + 20 is a lot like 5 + 2.

We have been working even more with this by using the frogs Tad and Pollie on a lily pad number line.  With this, we see how many jumps it takes to get to a fly…but also work with what it means for each jump to be 10 inches.  We will be working more with that over the next days!