Tag Archives: Fractions

Number Talks – Fractions

12 Replies

Through doing Number Talks with students K-5, I started to realize that one thing I look for students to use in our whole number computation discussions is using known or derived facts to come to a solution. I feel like the problems I have been using are crafted to use the answers from previous problems to reason about the ending problem.

In the younger grades, I would like to see students using the double known fact of 7+7=14 to know 7+8=15. I want them using 23 + 20=43 to get 23 +19 = 42. I don’t want them treating every problem as if they have to “start from scratch” adding all or adding on.

An example in the upper elementary:

18 x 2

18 x 20

18 x 19

This progression leads them to use a known or derived fact (18 x 20) in order to solve 18 x 19. To build efficiency, I don’t want them to the treat the final problem in the progression as a “brand new” problem in order to reason about an answer.

Along these lines of thinking, as I observed students working the other day, I realized that students weren’t using this same use of known/derived facts when working with fractions. For example, a student was adding  3/4 +  7/8. He used 6/8 as an equivalent of 3/4, added that to 7/8 and ended with an answer of 13/8. Don’t get me wrong, I loves his use of equivalency and I am a fan of improper fractions, however I started wondering to myself if it would have been more efficient (or show that he actually thought about the fractions themselves) if he used a fact he may have known such as 3/4 + 3/4=1 1/2 to then add an 1/8 on to get 1 5/8? Or used 3/4 + 1 = 1  3/4 and then took away an 1/8? Is that the flexibility I want them using with fractions like I do with whole numbers?

I thought I would try a Number Talk the following day to see….

1/2 + 1/2

Thumbs went up and they laughed with a lot of “this is too easy”s going around.

1/2 + 1/4

Majority reasoned that 1/2 was the same as 2/4 and added that to 1/4 to get 3/4. Some said they “just knew it because they could picture it in their head” I asked if anyone used what they knew about the first problem to help them with the second problem? Hands went right up and I got an answer that I wish I was recording. It was to the effect of,”I know a 1/4 is half of 1/2 so the answer would be a 1/4 less than 1.”

1/2 + 3/4

Thumbs went up and I got a variety here. Some used 2/4 + 3/4 to get 5/4 while others decomposed the 3/4 to 1/2 + 1/4, added 1/2 + 1/2=1 and added the 1/4 to get 1  1/4.

3/4 + 3/4

Got some grumbles on this one, because it was “too easy” – 6/4…Duh! The class shook their hands in agreement and they were ready to move on to something harder.  I noticed that when the denominators are same, they don’t really “think” about the fractions too much. I waited….finally a student said, “It is just a 1/4 more than the previous problem so it is 1  1/2″ and another said each 3/4 is 1/4 more than a 1/2 so if you know 1/2 + 1/2 = 1 then you add 1/2 because 1/4 + 1/4 = 1/2.” I had to record that reasoning for the class bc it was hard for many to visualize.

3/4 + 5/8

Huge variety on this one and I thoroughly enjoyed it! From 6/8 + 5/8 = 11/8 to decomposing to combine 3/4 and 2/8 to get the whole and then 3 more 1/8s = 1 3/8.  There were many more students who used problems we had previously done.

What I learned (and questions I still have) from this little experiment:

– Students LOVE having the same denominator when combining fractions.

– Do they really “think” about the fractions when the denominators are the same? Can they reason if that answer makes sense if they are just finding equivalents and adding.

– Students can be flexible with fractions if you push them to be.

– Subtraction will be an interesting one to try out next.

– I would much prefer if I remembered to use the word “sum” instead of “answer”…. I tell myself all of the time, but in the moment I always forget.

– Using known or derived fact and compensation are invaluable for students when working with both whole numbers,  fractions and decimals.

– Are there mathematical concepts that present themselves later in Middle School or High School in which known and derived facts would be useful?

Happy Thanksgiving,

Kristin

Fraction of Fraction Day 2

Leave a reply

As I mentioned in my previous post: https://mathmindsblog.wordpress.com/2013/11/15/fractions-of-fractions/ 
I had wondered about fraction multiplication being introduced without a context when the students were coming from lessons in which a fraction of a whole/mixed number had a context. Feeling like the students had a solid grasp on how to find a fraction of a fraction on a fraction bar, I thought I would try having them develop a story context for fraction multiplication problem. They had free reign of the fractions they used and context they chose. Needless to say, it was a learning experience for me. Some showed understanding of what they were doing when finding a fraction of a fraction of something while others unveiled some things I need to go back and revisit.

I have included clips from some of their videos and what I learned from each…. (turn your volume up bc they whispered on these)

http://www.educreations.com/lesson/view/aiyana-fraction-bars/13628710/?s=fv1sHe&ref=link

This one was SO interesting (and a little humorous) because she cut the fraction bar to find 2/3s of 1/2, however when she is explaining her reasoning she used the commutative property. Saying that the answer is 2/6 because that is half of 2/3 was something I had never thought of exploring with students when reasoning about whether the answer made sense. I loved it and definitely added to my lessons for next week!

http://www.educreations.com/lesson/view/riley-s-breadstick-word-problem/13630693/?s=j3i9i5&ref=link

When she introduces the scenario, she says “1/2 of 1/4” so I don’t know if she misspoke or not really understanding the context. I can see she has the process but I don’t know if the understanding is there. I do love how she says “He wanted to find how much of the whole bread stick that was” because she is relating her answer back to the whole. This was difficult for many students. Maybe picky on my end, but I would have liked for her to label the pieces 1/8, 2/8, etc instead of by whole number, even though I know she is counting the pieces.

http://www.educreations.com/lesson/view/ab-word-problem/13627803/?s=Hr3zRv&ref=link

I was impressed how she used a class of students as the whole and did not get confused with the fraction of the class as opposed to the number of students. Many others got caught up in “How many students…” instead of “What fraction of the class.” One thing that just bothered me in watching it was the empty seat in the class! I just wanted to draw a person in for her!

http://www.educreations.com/lesson/view/kyra-s-problem/13628055/?s=aIYKAt&ref=link

This one has such a great context and division of the Hershey Bar that I was so excited, until the end. She seemed good with the context, decontextualized to solve, but then struggled to recontextualize to explain the answer.

I could post and comment all day, but needless to say there is other work to be done and papers to be commented on! It was a great first day with our 1:1 iPads using Educreations! I learned so much that now I must work on readjusting my math plans for next week!

-Kristin

Why We Need Two Teachers in Every Classroom…

2 Replies

This job takes two brains to handle the thoughts of these students.

In class on Friday, one student made the comment that he didn’t really like adding fractions on the clock because it could only be used for certain fractions.  When I asked him to expand on that, he explained he could only do halves, 3rd, 4ths, 6ths, 12ths and 60ths easily and what if he wanted to do other fractions like 1/8 or 1/24?  He said he couldn’t do that without breaking the minutes up.  I am excited at this comment especially because this student is one whose parents have taken him to Kumon math for years for “extra help” and he is most comfortable memorizing procedures over thinking about the math. He thinks changing to “common denominators by multiplying the numerator and denominator by the same number” is faster and easier than this clock.

Upon reflection, I think it is interesting that he stayed with fractions of the fractions we were working…why not pull out 1/9 or 1/11? But my first train of thought in the moment was changing the whole. I wanted to see if he could put the clock in terms of a whole day, 24 hours, 2 rotations around the clock being the whole instead of one. That way 8ths and 24ths would be more apparent.

So I asked him if he could think of a way we could change the clock to do 1/8 or 1/24 without breaking up minutes? His first reaction was no, so I said “That is interesting because there are 24 hours in a day, so I feel like this should work.” Possibly leading him too much but at that point I could see the glazed look in some of the students eyes and I felt like I was losing the class’ attention. I told him that during math workshop that day he could chat with me about it or he could take that thought and work with some more for Monday.  He said he wanted to think about it over the weekend…I think mainly because he didn’t want to miss the Math Workshop activities, so we will see what he has for me tomorrow.

After school, I am recapping this lesson for Nancy and saying how difficult I thought it would be for them to grasp two rotations of the clock as the whole for the 24 hours that would allow for 8ths and 24ths more easily.  After listening to me ramble for about 5 minutes about this idea, she casually says, “What about military time?” UMMMmmm…DUH. Where was she during that class period??  This job really does take two brains.

So needless to say, I have amended my lesson for tomorrow. I am handing them this military clock and letting them talk about what fractions we can work with easily that are the same as our first clock and which one’s are different. Design addition equations we can solve with this clock that we couldn’t do on the other clock without breaking minutes.

Image

Don’t get me wrong, I still want to get to changing the whole on our original clock, but I think after working with this clock, it may be more accessible for more of the students. I will post later to update on this lesson to show how it went…but good or bad, the questions and thinking that led to this lesson are so worth it!

-Kristin