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Q&A #495

Teachers' Lounge Discussion: Rounding numbers to the nearest ten

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From: J. Douglas <jdouglas@icsd.k12.ny.us>
To: Teacher2Teacher Public Discussion
Date: 2001082415:33:48
Subject: Re: rounding numbers to the nearest ten

 I have worked with third- and fourth-graders on rounding and have
found that using a 0-99 chart (1-100 is OK, too) works well,
especially for children who don't have the abstract place value
concepts yet.  Use crayons!  First fold or draw a dark line down the
middle of the chart, between the numbers with 4 in the ones place and
the numbers with 5 in the ones place.  Color the "numbers you say when
you count by ten" a nice, bright color.  Then color the numbers with
1, 2, 3, and 4 in the ones place one color, and the remaining numbers
(with 5, 6, 7, 8, 9) another color.  Use this chart to locate a number
to be rounded, identify which ten numbers it is between, and choose
the number to round to by color and by seeing which ten number is
closer. Some children will want to write the ten numbers on the right
side of the chart to reinforce which numbers the number to be rounded
is between.  Having the chart in color is a big help for kids who
don't readily see patterns in the numbers.

The baseball/softball analogy works very well with kids who round down
by skipping a ten: 42 rounds DOWN to 30 (because you go to the next
lowest ten).  Unfortunately, a lot of third and fourth graders make
this mistake.  Tell them that in baseball, you can advance to the next
base or stay, but you can never go back to an earlier base.  If you're
on first, you can take a lead and think of stealing second.  If the
pitcher attempts to pick you off, you head back to first.  If the
coast is clear and you have a good lead, you take off for second.  You
can never go back to home.  So, rounding numbers is just like
baseball.  If you have a good lead (at least half way there), you go
to the next base (ten or hundred).  If you're only a few steps off the
bag, you stay at that base.  You can call out a number and have kids
call out STAY or GO.  When there is consensus on that, the kids get to
round.  
  

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