Q&A #495

Rounding numbers to the nearest ten

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From: Gail (for Teacher2Teacher Service)
Date: Aug 19, 1998 at 21:20:35
Subject: Re: Rounding numbers to the nearest ten

It is important that this student first be able to skip count by tens and by
hundreds, since those are numbers he/she will be using when rounding.  Then,
it is important that he/she knows what "consecutive" tens, or hundreds are.
You can have the student work with number lines, beginning at amounts greater
than zero, to practice skip counting.

After you have created number lines, ask the student to select two
consecutive amounts and put a dot where he/she thinks the midpoint is (the
spot directly in the middle between those two tens or hundreds.  Help him/her
label that point.  Do this with all the tens or hundreds on the number line.
 Help the student see there is a "pattern" for all the middle points.

When your student is comfortable finding midpoints, ask him/her to choose a
number that has not been marked on the number line (for example, 63).  Ask
the student to figure out where it belongs on the number line.  (He/she
should place it on the line between 60 and 70, before the midpoint of 65.)
By using the line segment between 60 and 65 as a guide, the student can see
that the point for 63 is much closer to 60 than it is to 70...   so the
number rounds off to 60.

If you are rounding to the nearest hundred, select a number like 178, and
look for the two consecutive hundreds it is between. The student should place
it between 170 and 180, past the midpoint of 175.  Using the line segment
from 170 to 180 as a guide, the student can see that 178 is closer to 180
than it is to 170, so that amount rounds to 180.

If you find the number is the midpoint, tell the student they are exactly
halfway between the two consecutive tens or hundreds, so there really isn't
a "closer" one to go to...   usually the way to round such a number is to go
"up" the number line to the higher of the two  (sometimes, if you are doing
an estimate, this will cause your sum to be way off...   but that is really a
consideration for students older than fourth grade...)

Repeat this many times, until the student can do the rounding mentally,
without having to resort to the number line.

-Gail, for the Teacher2Teacher service

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