## Friday, May 27, 2016

### Math problms of the week: Common Core-inspired "complete" vs. "incorrect explanations:

From Pennsylvania's PSSA Released items for 4th grade:

Pet peeve: "n times more than" != "n times as much as". If the new dog needs to eat 2 times more than food than the first dog, then the new dog eats 3 times as much food. So the first dog eats 1/3 cup, and the new dog eats 3*1/3 (or 1/3 + 2 * 1/3, if you prefer) = 1 cup. Therefore, both answers given are incorrect.

That said, if the test author really meant "twice as much food as", then I would be furious at having points taken off for the second answer. 1/3 IS the same as 2/6.

Anonymous said...

Once you develop good number sense around fractions, you tend to forget the verbiage that explains what you're doing in words (as opposed to arithmetical expressions). So someone with really good number sense will take longer to deliver the explanation that's expected here, and will feel frustrated by being expected to do this kind of explaining over and over.

Barry Garelick said...

Explaining your answer is something that Katharine and I explored in an article in The Atlantic. It didn't go over well in some quarters.