PURPOSE: The probability board will demonstrate the construction of a bell curve and will help students understand discussions of statistics.
NOTE: It is advisable that the board be teacher constructed for accuracy. Once the board is built is can be used yearly.
Labs done with the probability board should follow labs on outcomes with two variables, such as flipping coins, to ensure that students understand the basic concepts if predicting outcome. Labs should be followed with student conducted surveys and graphing.
MATERIALS:
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-large flat board at least 2” thick (size depends on how big a board is desired, the diagram depicts a board 15” x 11”)
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-thick cardboard or balsa wood cut into 1” wide strips
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-wood glue
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-nails
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-marbles (at least 20)
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-hammer
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-ruler
PROCEDURE FOR ASSEMBLY: (as shown in the diagram)
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Step One: Measure 1/2” from each side of the board, to create margins, side guards will be glued here to prevent run away marbles
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Step Two: Measure 1” wide columns, there should be 10 columns.
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Step Three: Mark off a line 6” from the bottom of the board. Below this line will become the marble catching area.
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Step Four: Measure 1” wide rows from the top to the 6” line. There should be 9 rows.
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Step Five: Place nails in the grid intersections as is shown in the diagram by the X marks.
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Step Six: Using the cardboard or balsa wood, glue diagonal top guards, side guards, and collecting columns as shown.
DEMONSTRATION:
Set the board on a notebook to create a slight tilt. Experiment with the slope so that the marbles roll, but not too fast. Drop the marbles into the top and let them find their own path to the bottom. If the bell shape is not produced, check the placement of the nails.
When doing labs with the probability board it may be helpful to have a diagram of the board on an overhead projector so that the route of the first few marbles can be mapped. Encourage student predictions throughout the labs. Perfect bell curves may not be formed, but students should be able to see the general shape. More marbles will produce a clearer shape.