Valuing misconceptions on the way to explaining fractions

26 Nov

explaining fractions_0001.wmv
Watch on Posterous

I filmed this about 6 months ago, following an excellent session about fractions on the Mathematics Specialist Teacher Programme. The challenge that we were given, and then I in turn gave to the children, was given a 4-pint bottle of milk that gets 3/5 of a pint drunk each day, how many days does the milk bottle last for? Those of us with a formal background in maths would say:

÷ 3/5
= 4 ÷ 3 x 5
= 4 x 5 ÷ 3
= 20 ÷ 3
= 6 r 2.
So the milk lasts for 6 and a bit days. If we wanted to be really fancy we would say the milk lasts for 6 and 2/3 days. And isn't it more practical to say the milk lasts for 6 days and there's 2/5 of a pint left over? Does our understanding of the algorithms let us say that?

Also can children, who are without the drilled-in knowledge that when you divide a divisor you actually multiply, do this question?

That's what the video explores – and there's some interesting misconceptions on the way.

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