Scuff Posted October 10, 2013 Share Posted October 10, 2013 Help me think this through. I just found out (how did I not no this sooner?!) my son is doing subtraction left to right. He starts with the left place and writes the answers, going back to change the previous answer down one if he has to borrow. So, if he's doing 403,712- 215,213, He will start with 4-2, write 2, move to 0-1, change the 2 to a 1 and then solve 9-1, write 8, move to 3-5, change his 8 to a 7 and then solve 13-5, etc. I need to fix this, right? He gets the write answer, but it's kinda crazy how he gets there. Is there a reason it would be ok to let him continue doing it this way? Will this screw him up in higher maths? (I went through Calc 2, but that was a long time ago!) He needs to learn to go rt to left, right? Quote Link to comment Share on other sites More sharing options...
Cosmos Posted October 10, 2013 Share Posted October 10, 2013 This is actually a very efficient way to do subtraction. I bet he can do it quickly, right? I would teach him the right-to-left algorithm because no doubt he will see others using it, but let him choose his own method. In higher math nobody will care how he does his arithmetic. Quote Link to comment Share on other sites More sharing options...
jennynd Posted October 10, 2013 Share Posted October 10, 2013 I won't.. as long as he get the right answer. Who cares Quote Link to comment Share on other sites More sharing options...
kiana Posted October 10, 2013 Share Posted October 10, 2013 There is nothing mathematically wrong with what he is doing. I tend to subtract left-to-right myself. Quote Link to comment Share on other sites More sharing options...
ThatHomeschoolDad Posted October 10, 2013 Share Posted October 10, 2013 Believe it or not, an ability to do math "backwards" like that will be a huge asset on the SAT. I wish more of my students were comfortable with it. Quote Link to comment Share on other sites More sharing options...
Farrar Posted October 10, 2013 Share Posted October 10, 2013 One of my ds does it this way if it's a shorter problem or if he's doing it in his head. It's a totally legitimate strategy - you're just regrouping at the end instead of the beginning. However, I would teach the traditional algorithm and make him practice it some. But then move on - as long he he gets it, I wouldn't be fussy about which strategy he continues to use. Quote Link to comment Share on other sites More sharing options...
Scuff Posted October 10, 2013 Author Share Posted October 10, 2013 Oh, wow. I just reread my post and can't believe the spelling mistakes. Ack! And I can't edit on the phone! I do know the difference between know and no and write and right. Goodness! Anyway, thank you! He'll be glad to know you all are on his side. ;) and it's reassuring to know I didn't mess him up! Quote Link to comment Share on other sites More sharing options...
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