Hi, I'm Heather Hook. I teach second grade at Northeast Elementary.Today
I'm going to model addition to one hundred using an open number line. If I have the problem
57 plus 43 I can use an open number line, which is a line without numbers to solve.
I will add numbers to the line as I work through the problem. To begin I will write the first addend
57, on the left side of the number line.
This is because I'm adding so my numbers will increase or get larger.
Next, I will decompose the second addend
43, which means to break it down into place value for tens and three ones.
I will represent the four tens with jumps and labels.
Plus 10 plus
10 plus
10 plus
10
57 plus 10 has the sum of 67, plus 10 has the sum of 77, plus 10 has the sum of
87, plus ten has the sum of 97. I will then represent three ones with smaller jumps and labels.
Plus one plus one plus one.
Ninety seven plus one has the sum of 98, plus one has the sum of 99, plus one has the sum of 100.
I will add my sum to the equation.
57 plus 43 equals 100.
Keep in mind there are many different ways I can add on an open number line. Another way would be to start at 57
look at the value of the four tens, which is 40. And make one large jump a plus 40.
Look at the value of three ones and make one smaller jump of plus three.
57 plus 40 has the sum of 97. Plus three more has the sum of
100. 57 plus 43 equals
100.
