FairProspects Posted April 18, 2013 Share Posted April 18, 2013 Now that ds has learned to do multi-digit multiplication in pieces, ds has been able to verbalize that this is the way he thinks about subtraction too. For example: 50 -17 ----- He says sees it as a whole like: 50 - 7 ------ 43 and then: 43 -10 ------- 33 instead of using the carrying algorithm and marking it up within the problem. The problem is that he struggles with math facts because of the dyslexia and cannot do the calculations all at once in his head like mental math so he really needs to write it out. He says writing the carrying algorithm just confuses him more because that is not how he visualizes it. Should I teach him to write this out on scratch paper as 2 separate problems so he can "see" the steps? Are there potential problems with him thinking about calculations this way? I was only ever taught the re-grouping/carrying/borrowing algorithm so I'm not sure if this is just a different method (I think it is, Singapore maybe?) or if is is really important that he be fluent with the traditional algorithm. He does understand the traditional algorithm, but doesn't like it or think it will work for him as a regular method. Should I let him do it this way or spend lots more time struggling with the regular algorithm? My tendency is to let him go with it since it seems to be a valid strategy for multiplication. Quote Link to comment Share on other sites More sharing options...
Pen Posted April 18, 2013 Share Posted April 18, 2013 His strategy is valid. How does he handle it if there is a problem with longer numbers. (5012 - 1736 = ) There may come a time when he'd like to know the other way for convenience, but by then maybe it will be easier for him. Quote Link to comment Share on other sites More sharing options...
PeterPan Posted April 18, 2013 Share Posted April 18, 2013 You might look at the way RS teaches subtraction. It will be different from his method (which is of course valid but tedious for long problems) but might work for him. In a nutshell, it has you do the subtraction from the LEFT. You go through and do all the trades first, then you do the actual subtraction, left to right. They explain it in level C or you can get the lessons from the Transitions manual (the cheapest way if that's all you need). RS actually teaches a few more ways to do subtraction in level C. They're alternate versions, like your ds is pursuing, that break it up into steps and think through the numbers as quantities. My memory fails me, but I think they had a few alternate methods for multi-digit multiplication as well. He might like to explore them, just to examine whether he can be mentally flexible, try several methods, and come back to the one that's easiest for him. Also, make sure it's not a *working memory* issue as opposed to how he thinks through math. Indeed doing all the trades (what RS calls them, essentially borrowing) FIRST can help with that. It's less to process all at once. My dd never stumbled over 4 digit subtraction once she got it. Well we took forever to get to that point, only doing 1 problem a day, haha. But when she had it it was fine. It was my favorite part of RS C. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.