mamamindy Posted January 15, 2015 Share Posted January 15, 2015 We've used Singapore from the beginning - Primary Math, Standards Edition - but *I* am having trouble explaining some of these mental math strategies to DD. I could use extra steps, I guess. We're at the beginning of 3A, using mental math strategies for addition and subtraction, like when a number is close to 100, or 10. An example of a problem: 970 - 97 We're to subtract 100, and then add back in the 3 ones, for a two step mental process: 970 - 100 + 3. The problem is, just a page before we were doing the same thing with addition, 970 + 97 = 970 + 100 - 3, and my DD is getting frustrated remembering whether to add or subtract the 3 ones. I mean, I get it, but even I fumble (especially in math!) when doing it quickly...and have a fuzzy moment. (If it's not obvious already, I'll just say, I'm not a math person, but I have really appreciated SM - I love it - and I'm learning a lot.) Just wondering what sorts of tricks you use to make this SUPER CLEAR when teaching these sorts of strategies? While writing this out I realized that I could just first illustrate - very concretely - that 97 is the same as 100-3. FTR we use rods with our lessons and I always make sure she can use them if she needs them. Then maybe when we write it out on the white board I can re-clarify, in a different color or something.... Quote Link to comment Share on other sites More sharing options...
Minerva Posted January 15, 2015 Share Posted January 15, 2015 I "liked" your post because I think you did a fine job answering your own question. Also, maybe you could do the some sample problems like 970-99 and 650-99, 330-98...working your way to more difficult numbers. We don't use Singapore, so perhaps you already do this, but it might just be a case of a little more practice. I am loving doing mental math with my nine year old. I have never been good at it but am getting so much better. Quote Link to comment Share on other sites More sharing options...
Tanikit Posted January 15, 2015 Share Posted January 15, 2015 I used manipulatives (the tens and hundreds bars and squares with indivdual blocks shown on them) - then you say - we want to subtract (or add) 97 to the first number. That is pretty close to 100 - so lets subtract/add 100 - ok, but you didn't want to subtract/add this whole hundred block did you - you have taken away too much/subtracted too much - so you need to fix it - you added 3 too many so you need to remove/subtract those 3 - or you subtracted 3 too many so give them back/add them back. When they are seeing it, it is easier to understand. Quote Link to comment Share on other sites More sharing options...
pitterpatter Posted January 15, 2015 Share Posted January 15, 2015 Yes, I wish there was a chart. I've not looked (but haven't noticed any either), but it would be great if Singapore would offer a pack of chartlets for each level. My DD does not remember (more like pay attention enough to give herself a chance to remember) a lot of the time-saving strategies either on her own. I wish I had an easy-to-read eye-catching chart for the wall where she could double-check for these types of strategies. This is also a reason I've been hesitant to sell off my old HIGs. I'm afraid I won't remember how to do or explain something. Quote Link to comment Share on other sites More sharing options...
SparklyUnicorn Posted January 15, 2015 Share Posted January 15, 2015 I've had to talk the strategy out about 5000 times before my son started trying to use it. Just saying it isn't necessarily something they get right away. You might like Math in Focus. They break stuff down even more than PM or Standards. Quote Link to comment Share on other sites More sharing options...
HelenNotOfTroy Posted January 15, 2015 Share Posted January 15, 2015 I have been watching the videos on Education Unboxed to help with teaching this sort of thing. Quote Link to comment Share on other sites More sharing options...
sweetpea3829 Posted January 16, 2015 Share Posted January 16, 2015 I'm listening in for strategies because... Yesterday my son asked me why I use a calculator to check his schoolwork... :leaving: Quote Link to comment Share on other sites More sharing options...
kateingr Posted January 16, 2015 Share Posted January 16, 2015 I definitely agree with the above posters about working up to it with 99s and 98s, and also using manipulative so to walk through the steps. My only other thought is to not rush it. The strategies are certainly helpful for mental math, but the hard thinking that kids have to do to figure it out is just as valuable. It's not about memorizing a certain procedure, but about kids having the confidence that they can think through problems and figure them out. So no worries if it takes your ds a while to really get it. Quote Link to comment Share on other sites More sharing options...
SparklyUnicorn Posted January 16, 2015 Share Posted January 16, 2015 I'm listening in for strategies because... Yesterday my son asked me why I use a calculator to check his schoolwork... :leaving: :ohmy: Quote Link to comment Share on other sites More sharing options...
SevenDaisies Posted January 16, 2015 Share Posted January 16, 2015 I don't think there is an easy way to remember, but teach them to think about it logically. After you add the 100 ask 'Have you added too much or too little?' or after you have subtracted the 100 ask 'Have you subtracted too much or too little?.'' Then figure out from there- if I added too little I add it back, if I added too much I subtract, if I subtracted too much I add it back and if I subtracted too little I subtract it back. Quote Link to comment Share on other sites More sharing options...
wendyroo Posted January 16, 2015 Share Posted January 16, 2015 We use the Singapore MathExpress Books to work on mental math strategies, and I encourage DS to use their bubble notation to mark how he is breaking the numbers apart. For example, in this sample they show 116 being broken into 120 and -4. After he has done a few problems writing out the bubbles, then I have him progress to just verbally telling me what would be in the bubbles, and then he is eventually ready to just think the bubbles and complete the calculation. Wendy Quote Link to comment Share on other sites More sharing options...
letsplaymath Posted January 16, 2015 Share Posted January 16, 2015 I don't think there is an easy way to remember, but teach them to think about it logically. After you add the 100 ask 'Have you added too much or too little?' or after you have subtracted the 100 ask 'Have you subtracted too much or too little?.'' Then figure out from there- if I added too little I add it back, if I added too much I subtract, if I subtracted too much I add it back and if I subtracted too little I subtract it back. Mental math is applied common sense. Don't worry too much about the steps, but focus on how to understand the numbers. See if you can compare them to "friendly" numbers that are easier to work with, and then make the appropriate adjustment to get the actual answer required. I describe several ways to approach a problem in my blog post Mental Math: Addition, but the same principles apply to subtraction, multiplication, etc. Quote Link to comment Share on other sites More sharing options...
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