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4.6.3 Estimating Cranberries



4.6_Frame-2-50x50.jpg  Estimating Cranberries (video)
Students estimate the number of cranberries rather than the number of scoops.

Video Segment

The lesson continues with the teacher's asking the students to think about how they would estimate the number of cranberries in the jar. The groups work to determine a value that represents the number of cranberries in a scoop and how to use that value to estimate the number of cranberries in a jar. The class comes back together, and each group shares its value for the number of cranberries in a scoop. These values range from twenty-one to twenty-eight cranberries per scoop. In this last video segment, the students talk about how and why they have come up with different values for the number of cranberries in a scoop and what single value the whole class might use as the number of cranberries in a scoop.


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 ----- Transcript Begins ------

Teacher:  If we are all using cranberries, how
can we come up with a different answer? Timmy?

Timmy:  Because that, um, a cranberry, one of
the cranberries, could be bigger than another.

Teacher:  Yeah.

Timmy:  Or you could have, um, put it over a
little or under a little.

Teacher:  That's right.  Some are bigger, some
are smaller. That's just how things work in
nature, so Timmy is exactly right.

------ Transcript Ends   -----

Download Video 

  

----- Transcript Begins ------

Teacher:  What would be an average if we had
between twenty-one and twenty-eight?  How could
we say, like, well the average number was...?
What would you say it could be?

Boy 2:  Twenty-six.

Teacher:  And why do you say that?

Boy 2:  Cause, um, there's, there's two twenty-
sixes and one and just one of the other numbers.

Teacher:  Okay, and is there any other reason?
There are more twenty-sixes than the others.
Emma, what do you think?

Emma:  It could be like twenty-five because
twenty-one is farther is like pretty far apart
than twenty-eight and twenty-six and twenty-eight
are only separated by one.

Teacher:  Um, huh.

Teacher:  So here we say this is the here is our
range.  We have between twenty-one and twenty-
eight.  That's what you're saying. And if we went
in to the middle, it would be about twenty-five.

------ Transcript Ends   -----
 

Discussion

Teachers can help students develop estimation skills by planning slightly varied versions of activities, so that students are likely to recognize that strategies that were successful in one situation may be helpful in the new tasks.

The discussion of an average number of cranberries in a scoop ends with the selection of a value of twenty-five. The teacher then relates the counting of multiple scoops to the skip-counting used when counting quarters to add up to a dollar. The class uses this counting technique to determine that it takes approximately 300 cranberries to fill a jar.

Take Time to Reflect 

  • What mathematical ideas from number, geometry, measurement, and data do the students use to complete the activities in this lesson?
  • How does the teacher encourage the students to make mathematical connections?

Video Credit

Roche, Robert . "Cranberry Estimation." In Estimating produced by WGBH Boston. Teaching Math, A Video Library, K–4. Funded and distributed by the Annenberg/CPB Math and Science Project, P.O. Box 2345, S. Burlington, VT 05407-2345, 1-800-LEARNER. 


 Also see:  

  • 4.6  Developing Estimation Strategies by Making Connections Among Number, Geometry, Measurement and Data Concepts

    • 4.6.1  Estimating Scoops
    • 4.6.2  Discussing Strategies

      • 4.6.2a  Discussing Strategies Extension
     


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