Fraction calculator: 1/2 : 1/3

     

Several years ago, I was working with a class of fourth and fifth graders. Their teacher had begun a unit on fractions & was interested in connecting fractions lớn real-world contexts. “No problem,” I told her.

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Our plan was that I would teach a lesson, she would observe, & then we’d revisit it. I’d focus on talking with students about naming fractional parts, the standard symbolism of fractions, và equivalence.

My first real-world context: a six-paông chồng of water

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I showed the class the six-pack I had brought lớn class and talked about one bottle being 1/6 of the six-pack, two bottles being 2/6, three bottles being 3/6, và so on up lớn 6/6 being the same as the whole six-pachồng. The students seemed comfortable with this, & I wrote the fractions on the board:1/6 2/6 3/6 4/6 5/6 6/6

We also talked about three bottles being one-half of the six-paông xã, and that 3/6 và 50% were equivalent fractions because they both described the same amount of the six paông chồng. I recorded this:3/6 = 1/2

I asked what fraction of the six-paông chồng would be gone after I drank four of the bottles & they answered 4/6 easily. I represented this numerically:1/6 + 1/6 + 1/6 + 1/6 = 4/6

I asked what fraction of the six-paông chồng would be left after I drank four bottles, và they answered 2/6 easily. I represented this numerically with two equations:6/6 – 4/6 = 2/61 – 4/6 = 2/6

My second real-world context: a box of 12 pencils

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I continued with a different context—a box of 12 pencils. We talked about one pencil being 1/12 of the box, two pencils being 2/12, three pencils being 3/12, and so on. I wrote these fractions on the board:1/12 2/12 3/12 4/12 5/12 6/12 7/12 8/12 9/12 10/12 11/12 12/12

The pencil box gave us a way to lớn talk about another equivalent fraction for 50%, this time 6/12. And I talked about 12/12 representing the pencils in the whole box:6/12 = 1/212/12 = 1

I asked, “If I give sầu a pencil khổng lồ each of five students, what fraction of the pencils would I have sầu given away?” They answered easily và I recorded numerically:1/12 + 1/12 + 1/12 + 1/12 + 1/12 = 5/12

I asked if 5/12 represented more or less than half the box, và they agreed that it was less than half. I recorded again:5/12 Then I hit a snagThe students in this class sat in small groups, và I next called the students’ attention to lớn a table where two boys and one girl were seated. I asked them what fractional part of the students at the table were girls. Hands shot up & I had them say the fraction in unison in a whisper voice—one-third. I wrote 1/3 on the board.

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Brad noticed that the table next to lớn his also had two boys and one girl sitting at it. Claudia commented, “So if you put the two tables together, then 2/6 would be girls.”

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Addison’s hand shot up. “Can I come up & write that in fractions?” he asked. I agreed. Addison came up and wrote on the board:1/3 + 1/3 = 2/6

I was stunned. Addison was correct that 2/6 of the students at the two tables were girls. But the addition equation that Addison wrote wasn’t correct. It’s every teacher’s nightmare when students combine the numerators và denominators to add fractions & think that adding 1/3 and 1/3, for example, gives an answer 2/6. But I didn’t think that Addison had applied that incorrect procedure. I wasn’t sure exactly what he was thinking.

To buy some time, I asked Addison lớn explain what he had written. He said, “One out of three at Brad’s table is a girl, so that’s one-third. And it’s the same for Margaux’s table. So, if you put them together, then two out of all six kids are girls, và that’s two-sixths.” The rest of the students nodded.

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They were all pleased. I was a wreông chồng.

So much for buying some time.

It’s hard khổng lồ think & teach at the same time!I stood quietly và thought for a moment about what lớn bởi vì next.

To fill the quiet, I said to the class, “When thinking about fractions, it’s important khổng lồ keep your attention on what the whole is.”

They nodded politely.

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After thinking some more, I returned to lớn the context of the two tables of students. I said to Addison, “I see that you’re thinking about the two tables together.” He nodded. “So, the group of students at the two tables together has six students.” He nodded again. “Then Brad, Samantha, Jaông chồng, Margaux, Robbie, and Max, are each 1/6 of that group, just as each bottle of water is 1/6 of the whole six-pachồng.” Another nod. And because 1/6 + 1/6 equals 2/6, it makes sense to me that 2/6 of that group of six are girls.” I wrote on the board:1/6 + 1/6 = 2/6

None of the students seemed concerned that 1/3 + 1/3, as Addison had written, seemed to lớn produce the same answer as 1/6 + 1/6, as I had written. Now I was breaking out into a sweat.

I tried again lớn explain“Let’s look at just one of the tables,” I suggested. “There are three students—Brad, Samantha, và Jaông xã. What fraction of the table does Brad represent?” The students answered 1/3 easily. “And what fraction does Jack represent?” They answered 1/3 again. “And what fraction of the table are boys?” They answered 2/3. I wrote on the board, underneath what Addison had written:1/3 + 1/3 = 2/61/3 + 1/3 = 2/3


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