don steward
mathematics teaching 10 ~ 16

Friday, 28 January 2011

multiplying decimals

what is
0.3 x 0.4
0.7 x 0.4
0.3 x 0.6
0.7 x 0.6
and why?

it seems to me that an attempt to explain decimal multiplication in terms of 'decimal places' needs a firmer foundation...

there are slight anxieties about this model because the 'unit' shifts  from being of a length (side of the square) to of an area... just as well that 1 x 1 is still 1...

No comments: