2 ms·

Some random gis image. http://i.imgur.com/RvAUuPK.jpg http://i.imgur.com/RvAUuPK.jpg Compare that to how you could solve the problem in your head. .01 + .70 +

by parfe 12y ago

Some random gis image. http://i.imgur.com/RvAUuPK.jpg http://i.imgur.com/RvAUuPK.jpg Compare that to how you could solve the problem in your head. .01 + .70 + 6.00 For my example I bet you'd think 5¢ + 50¢ + $5.00 to compute your change.

parennoob 12y ago
Firstly, I think you probably mean +0.01 +0.70 +6.00 Also, when you say the +0.01 and +0.70 there, aren't you implicitly borrowing anyway? It's just "easier" borrowing -- you say that 0.09 + 0.01 = 0.10, as opposed to explicitly borrowing the 1 to the second decimal and subtracting the 9. Similarly, you say that 0.30 + 0.70 = 1.00 instead of borrowing the 1 to the first decimal. I can see why this makes mental maths easier, but I don't see that it is any deep conceptual improvement over the borrowing. Is one of the goals of Common Core to improve mental arithmetic? If so, then this makes sense. Otherwise, unless you properly explain why the two are equivalent, and why the other method is faster, it's more like a neat sleight-of-hand trick that might leave kids slightly more confused about why it is "better" than the borrowing method. [Reference: Non-American, non-parent who knows very little about the American education system, but has some friends teaching in it.]
- deleted 12y ago
  [deleted]
- parfe 12y ago
  Fixed, thanks. All math solutions will be equivalent. And it isn't a parlour trick. It's teaching kids to think about breaking down problems into smaller units and composing a solution. The rote algorithms work, but training kids to execute an algorithm won't help them understand. The long form subtraction algorithm isn't a skill that carries over to multiplication. Breaking a problem into smaller components, composing a solution, and checking with your original estimate does carry over. And not just multiplication but programming as well.

by parfe 12y ago

parennoob 12y ago

Firstly, I think you probably mean +0.01 +0.70 +6.00 Also, when you say the +0.01 and +0.70 there, aren't you implicitly borrowing anyway? It's just "easier" borrowing -- you say that 0.09 + 0.01 = 0.10, as opposed to explicitly borrowing the 1 to the second decimal and subtracting the 9. Similarly, you say that 0.30 + 0.70 = 1.00 instead of borrowing the 1 to the first decimal. I can see why this makes mental maths easier, but I don't see that it is any deep conceptual improvement over the borrowing. Is one of the goals of Common Core to improve mental arithmetic? If so, then this makes sense. Otherwise, unless you properly explain why the two are equivalent, and why the other method is faster, it's more like a neat sleight-of-hand trick that might leave kids slightly more confused about why it is "better" than the borrowing method. [Reference: Non-American, non-parent who knows very little about the American education system, but has some friends teaching in it.]

deleted 12y ago
[deleted]
parfe 12y ago
Fixed, thanks. All math solutions will be equivalent. And it isn't a parlour trick. It's teaching kids to think about breaking down problems into smaller units and composing a solution. The rote algorithms work, but training kids to execute an algorithm won't help them understand. The long form subtraction algorithm isn't a skill that carries over to multiplication. Breaking a problem into smaller components, composing a solution, and checking with your original estimate does carry over. And not just multiplication but programming as well.