Rounding Numberline

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Home : 2001 : September : 2

Rounding Numberline
By Alison

The most effective way I have found to teaching rounding is with the use of a roller coaster type numberline. Draw a series of connected up and down lines like mountains ^^^^^^^ . To round to the nearest tens, label the points:
5, 15, 25, 35, 45, 55, etc. At the valleys, label them 0, 10, 20 , 30 , 40, 50 etc. Between 5 and 10 draw line segments to represent 6,7,8,9.
To use this numberline, I have the students imagine I am holding a marble. If the number I had to round to the nearest 10's was 6, I place my fingers on the 6 location. "If this was a hill, which way would the marble roll?" The students would

see it would roll downhill towards the 10. If the number was 24, it would roll towards the number 20. I tell them if the "marble makes it to the peak (5,15,25,...) then it automatically rolls to the next valley.
It is hard to explain with words, but I hope you get the idea. I can mail you a copy of one if you'd like.