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which strategy recommended for 2-digit adding?

Rosine, thank you so much for answering all the questions I've posted. Here's another though.

When asking ds to give the sum for 2-digit problems, I'm not sure which strategy RS would prefer we focus on, when the lessons don't mention any. This all concerns 2-digit adding in lessons 75 and beyond in Level B.

On pg 149, after doing a few 2-digit sums over 100 using the abacus, it then asks the child to add mentally 70+70, which I thought would depend on knowing the doubles (7+7) and adding a zero, which hasn't been covered yet ( unless I missed it?). But just know I'm thinking that maybe we were supposed to use the 2-fives strategy? (We're on Lsn 80, but I'm thinking back to some stumbling stones we had in lsn 75 + concerning sums over 100 mostly).

Then it asks for 47+70 mentally. Is that also to be done with 2-fives? If so, how is it broken out step by step? Like this ?: 50 + 10 + 10 + 40 + 7 = 50 + 50 + 17 = 117

Or is the child supposed to already know that 4+7= 11, adding zero = 110, +7 = 117?

Same for 66 + 80. Are we supposed to focus on 2-fives, 8's trick, or separating the tens and ones, or what?

On pg 150, it gives 86 + 39 with the mid-step answer and the final answer, but it doesn't give any breakdown as to how it should be done, and I don't know what to suggest or focus on? As far as I know, we haven't covered too many math facts over 10, atleast not to fluency, so how is child supposed to know that 86 + 30 = 116 if he doesn't already know that 8+3 = 11, unless using the 8's trick? Did I miss the lesson that covered adding the zero (tens) in cases that this?

How would RS break down the steps to doing 95+59?

Sums less than 100 don't give much trouble, but with like 28 + 37, ds doesn't like changing it to 28 + 30 + 7 for a mid-step of 58 + 7. He more automatically separates the tens and ones in both addends like 20 + 30 + 8 + 7 = 50 + 15, which seems clearer to me.

In lessons 76 - atleast 80, there are many practice problems (including in the warm-ups) with sums over and under 100, that do expect the child to work them mentally using the strategy taught in lsn 76 with an intermediary answer and a final answer. The intermediary answer based on keeping the 1st addend intact and breaking apart the 2nd addend into tens and ones. So this must be a better strategy than breaking all tens and ones apart in both addends? I just can't seem to get ds to think this way. Any suggestions?
thanks again!
Teresa

The strategy that your son feels the most comfortable with.

Teresa, It is perfectly fine for your son to add 47 + 70 as 40 + 70 + 7. Remember, there is more than one way to solve a problem. RightStart does a great job of presenting many different strategies that can be used to answer the same question which reinforces a child's ability to problem solve in the long run.

In RightStart you will never be told to add 4 and 7 and then add the 0 because this does not take into account place value. You will however be reminded to add 4 ten + 7 ten which equals 11 ten. 11 ten is the same as 110. Going over 100 for the answer can often be difficult when a child is first exposed to this. This is when it is helpful if you have two abacuses so he can actually physically add 4 ten + 7 ten and see how it is more than 100. He can certainly use the 2 fives strategy or the make 10 strategy that he learned for adding single digit numbers. If he understands place value the leap to understanding 4 + 7 = 11 isn't a big leap to understanding 40 + 70 = 110.

Does this make sense? I am a bit concerned that you are a little too concerned about the understanding and the knowing of how to do the 2 fives strategy. It seems to be bothersome. If this is the case just give it a rest for a while and continue to do the make 10 strategy and you and your son will be fine.

Please feel free to email or call me on the 888 line as well as continue to post your questions and concerns. I will be answering phones tomorrow morning so you are welcome to call and we can talk this through as well.

Teresa, I am most happy to answer any questions you might have. That's what I'm here for.

Sincerely, Rosine

Re: which strategy recommended for 2-digit adding?

I hope you don't mind my piping in here. My son also had trouble w/ the 2 fives strategy. I played war using only the 5-9 cards I think (it's listed in the games book) and that helped. The 2-fives wasn't natural for me either. I noticed about 2-3weeks after doing that lesson, that for certain problems, mainly involving 5s and 7s, he would use the 2-five strategy. It took some time to gel.

As far as 7+4. It helped my DS to think of that as 4ten+7ten=11ten. Eleven 10s is 110. You do need 2 abacuses(??) in order to demonstrate this. I showed DS numbers like 660 and asked "how many tens?" "66." Also, doing the 4ten+7ten on side B of the abacus but don't regroup ... just leave the 11 tens on the tens rod also helped.

What lesson are you on now? I found that during the next lessons: continuing the pattern, even odd adding rules, patterns up and down, money lessons,4 digit addition ... that DS cemented his 2-digit mental addition. Some days, maybe we only did the warm-up exercises. Also, I spread out the 4digit addition by having DS do just3 or so problems each, using the rest of the time to do some mental addition problems, play corners, and other games. He is now quite quick w/ 2 digit mental addition. I think the lessons after 2 digit mental addition are great for giving DC time to ruminate on those tough 2 digit mental addition lessons.

I will go back to warmups from previous lessons as well if I feel DS needs some review.

hth

Re: Re: which strategy recommended for 2-digit adding?

Yes, I'm glad to get your suggestions too. We're on lesson 80, and with all the various strategies taught in this level, I'm not always sure which strategy to emphasize, or which strategy ds is really using, or which one he needs work on. I have him show me his mental steps with the abacus or on paper, but it's hard for him to break down his steps. He likes to get straight to the answer. He also tends to use whatever strategy he's most used to, and doesn't like to learn new strategies if his older strategy works. The 2-digit addition is difficult for me because I never learned to do it mentally myself, and never learned any of these strategies either. So, I'm having to learn as I go, but hopefully I'll get it figured out before my next one is in level B. thanks again, Teresa

Re: The strategy that your son feels the most comfortable with.

Well, ds isn't too crazy about learning many different strategies. If he learns a strategy that works, then that's the one he always want to use with all problems. I have to really work with him to get him to try a new strategy.

As far as the 2-fives strategy goes, I've basically just not been sure as to how well RS lessons is expecting a child to know this or other strategies. We did lesson 79 today about making 100 from 99 and 98. DS finally got this strategy, but I had to break each problem down into steps using different strategies, one being his favorite of separating the tens and ones, so he could clearly see which strategy was easier (the newest one in this lesson). But then the worksheet for this lesson had a variety of problems to use a variety of strategies, and that's when I'm usually at a loss as to how to guide ds in his mental addition strategies, because sometimes I'm not sure myself which strategy would be best to use.

thanks again,
Teresa

The goal is to be exposed to as many strategies to help learn that there is more than one way to sol

Dear Teresa,

You will learn all of this before your teach Level B again. And, you will feel much more comfortable with it because you will have a perspective on it that you do not have right now due to the fact that this is your first time through it.

The goal here is to expose children to as many strategies as possible so they can have an understanding of the many different ways to solve a problem. Yes, he will choose what strategy works best for him.

Please don't worry so much about the 2 fives strategy. That strategy is based on one's ability to visualize the abacus, which we hope children do in their heads after they have had a sufficient of time to work with the abacus. Sometimes we have to invite our children to look at the abacus, close their eyes and then ask them what they see. If they say nothing then we have them open their eyes look at the abacus again, close their eyes and say "Try to see the abacus in your head." In other words, for some children we need to help them learn to "see" the abacus in their head. That goes for us too. Because for some of us we need to concentrate on how the abacus looks in our heads as well.

Sincerely, Rosine

Re: which strategy recommended for 2-digit adding?

Please pardon me butting into this conversation but I am so excited because reading your posts has helped a question finally crystalize in my mind. It is in reference to the children learning many different strategies from the beginning to solve math problems. When I taught ds to read, I first only taught him one sound for each letter (ex C sounding like K not S). Only once that was solid did I introduce variations. It seemed simple, one step at a time to me. I would assume the same would apply with learning to solve math problems -Do "X" it is straightforward and works, then when "X" is mastered to the point you can always fall back on it, then you can learn other ways to solve problems. Doesn't that make sense?
I like to think that it is an intelligent enough question that Dr Cotter atleast considered it at some point before making this math program. What I am hoping is that you can explain to me why I am wrong. I've read the results to see that I am wrong, but I'd love to understand why, I think I will be able to teach with much more confidence if I understand the reasoning behind this method :)