[Maths-Education] use of counterexamples in primary classrooms
romlins at rc.unesp.br
romlins at rc.unesp.br
Sat May 19 02:43:35 BST 2007
Dear Dylan,
indeed,
> Interestingly the same "method" of division features in Abbott and
> Costello's "In the Navy".
which is from 1941 and is at http://youtube.com/watch?v=HLuhPBuy6-0 (the
short scene). Ma and Pa Kettle seems to be from 1949, according to
imdb.org. Does anyone know how old this 'trick' is?
Anyway, I will show them both to my students!
Back to counterexamples. One could get Costello into possible trouble by
asking him whether 24 times 4 equals 24:
24
x4
--
8
16
--
24
Fourteen such cases if multiplying two-digit numbers by a digit. If ab can
be multiplied by some c1 to produce ab, so can ba by a c2, and
c1+c2=11...! :)
That reminded me of a friend, an excellent maths teacher, Bigode, who once
asked his 5th grade pupils to add 2/3 + 3/5 and got back the (natural)
answer 5/8. Instead of "correcting" them, he then invited them to list
properties this operation had: associative, commutative, it has an
identity element 0/0 and so on. For homework he asked them to do some more
additions. One of them was 1/2 + 1/2. That solved the supposed problem: a
half plus a half can't be but one.
all the best
Romulo
More information about the Maths-Education
mailing list