Q&A #445

Teaching subtraction and division to an adult


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From: Marielouise (for Teacher2Teacher Service)
Date: Jul 28, 1998 at 16:28:45
Subject: Re: Teaching subtraction and division to an adult

You should be commended for you concern and empathy for this person.  I have
never done this with an adult but have frequently talked this with young
children. I would approach this problem with manipulative such as beans or
chips as well as a calculator.

Starting with the basic binary sums for ten of 1 + 9, 2 + 8, 3 + 7, etc.  I
would ask that 10 beans or chips be separated into two groups and list the
combinations that make ten.   Part of the problem for an adult, as for a
child, is to make the transfer from the concrete to the symbolic.   Hence,
each visible group has a symbolic representation.  Having done the sums then
starting with ten, remove one of the parts to determine the part "left."
Do this with symbols as well.

Returning to the original sums of 1 + 9, 2 + 8, etc. I would change these to
11 + 9, 12 + 8 and see the same combinations only increase the original 10
chips by the 10 that were added to make 20.  I think that if the transfer can
be made to see that the additional ten can also be added to the 9 in 1 + 9 to
get 1 + 19 then any transfer to 30, 40, etc. can be made.   Practice with the
combinations of 20 - 1, 20 - 5,...

From there I would start with the teens:  12, 13, 14, 15, etc. up to 20 and
look at removing parts of them to see what is "left."

Where does the calculator come in?  I would use it as a check when asking a
question in symbols without the chips.

I really think that division is easier than subtraction.  It is based on
putting together a different number of groups of the same size group such as
three groups of 5 each.   This can be done using the calculator,  which 5 +
5 = 10, 10 + 5 gives 15.   Therefore three groups of 5 is 15.  Asking to
arrange the 15 chips in different number illustrates when there is a
remainder and when there is not.

I hope that this has given you some ideas.  If I have totally missed the mark
in answering this question; meaning, that I did not understand where you
needed help, write again.

 -Marielouise, for the Teacher2Teacher service

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