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This task is from Illustrative Math http://tasks.illustrativemathematics.org/contentstandards/4/OA/A/tasks/356 . It is a great site for all grade levels. This task is for grade 4:.OA.1 Here is the task for students: There are two snakes at the zoo, Jewel and Clyde. Jewel was six feet and Clyde was
eight feet. A year later Jewel was eight feet and Clyde was 10 feet. Which one grew
more? Then it gives the “Commentary” for teachers: The purpose of this task is to foster a classroom discussion that will highlight the difference between multiplicative and additive reasoning. Some students will argue that they grew the same amount (an example of “additive thinking”). Students who are studying multiplicative comparison problems might argue that Jewel grew more since it grew more with respect to its original length (an example of “multiplicative thinking”). This would set the stage for a comparison of the two perspectives. In the case were the students donâ€™t bring up both arguments, the teacher can introduce the missing perspective.