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How Many Beans
Objective: To introduce the concept of accuracy and significant digits.

Time Required: One 50 minute class period

Prior Knowledge:  Rounding whole numbers and estimation

Materials Needed: I bag of beans (pinto, navy, black, etc.)

Group size: 3 students

  1. Hold up a bag of beans and ask each group to estimate the number of beans accurate to the nearest unit.
  2. Record the guesses and discuss the accuracy of their guesses and the number of significant digits in their answer.
  3. Ask the students to mentally decide how much they would be willing to bet on the accuracy of their answer.
  4. Have the students round their answer to the nearest tens place and again discuss the accuracy of their guess and the number of significant digits.
  5. Have the students mentally decide if they would be willing to wager more or less money on the accuracy of their guess.
  6. Continue this process, rounding to the hundreds then the thousands place (if necessary).
  7. Distribute a portion of the beans to each group until the bag is empty, and have the students count the beans in their pile.  Compile the data from each group and tally up the number of beans in the bag.

Questions for Discussion:
  1. How many times more accurate is the guess to the hundreds (or thousands place) place than the guess to the tens (or hundreds) place?  The units place?
  2. How accurate is the count of beans in the bag?
  3. Describe the influences that could affect the accuracy of the count.
  4. How could the count be made more accurate?

C Adams

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