I wouldn’t go as far to say this is about making money. The intentions are good, but some things I’m just left scratching my head… Here’s an example. Here is the sort of common core math problems, that my kid has been practicing on a computer program that is being used by our school…
The problem is to solve a very simple subtraction problem 511-475…
The idea is to figure out which of the 4 methods to use the fewest number of “steps” to solve the problem…
Here are the different “methods
1)Method #1: The one of the far right is the traditional way of subtracting… Its suppose to take 5 steps…
…You borrow 10 to make 11, and subtract 5 to get 6 (2steps)
…You borrow 100 to and subtract 70 to get 30 (2 steps)
…You subtract 400-400 to get 0 (1 step)
2)Method#2: The one on the far left is called the “make 100’s/10’s/etc”.. Basically, you start with the small number and figure out how many hundreds it takes to get to the final number without going over… And then you add…Then you figure out how many 10’s it takes to get to the final number without going over, and then you add…Then you figure out how many 1’s it takes to get to the final number and add..
So for example,
a. starting at 475, you count by tens to get to 505… You get 30, and you add that to 475, which is 505.
b. Then you start at 505 and you figure out how many ones it takes to get to 511 (so that is 6)….
c. And then you add 30 with 6 ==> 36
This method supposedly takes 3 steps. Ok, I’m fine with this.
Method #3 and #4: The middle two “methods” I call the totally foobared methods because I’m trying to understand how either of them can be “easier” than either doing it the traditional way or the make 100’s/10’s/etc method….
3.Method #3: The method that is second from the right goes like:
a)take either number, and figure out how much it takes to get to a number that is “friendly” (base 100 or base 10)
511->500 : subtract 11
b)Subtract using the friendly number
500-475==>25 (supposedly kids are suppose to do this in their head…I doubt it…See my comment below)
c)add what you subtracted back to the answer
25+10 =>35
+1 =>36
5 total steps…Though I would disagree..If this problem was slightly different (say 511-476…The kid is not going to be able to do 500-476 in their head…They will end up subtracting 500-476 using the some traditional way, which defeats the entire point of this approach… Which is why imho I call this the method really foobared way of doing it.
4.Method#4: The method that is second from the left goes like
Shift each number on both sides by the same amount until you get a friendly number, and subtract the friendly number
So for example…475–>500
you first add 5 to both numbers (2 steps)
you then add 20 to both numbers (2 steps)
then you subtract the result (536-500) (1step)
5 total steps
Anyway, I timed my kid on doing the same problem each way….And the traditional “borrowing” method the results came out pretty quickly in my kid’s head, with a close second being the make 10’s/make100’s approach. I’m not sure what the point of the two approaches int the middle. I doubt most 3-4-5 graders could do that in their head…Which begs the question..WTF??? This is going to make kids have better math skills????
