An electrical probability teaching device has a rotary switch in which a brush contact connected to one side of a battery is rotated over a certain number of contact plates having surface areas proportioned in degrees of arc contacted by the brush according to known areas under the probability curve calculated for that certain number of divisions. Each contact plate is electrically connected through a resistor of a different value through a readout device so that different values of readout are obtained for the various plates on which the brush comes to rest. A checkerboard arrangement of a plurality of pins, arranged in rows and columns, in which each interior pin is connected by like resistors to each of the four pins adjacent to it vertically and horizontally, is used to teach the use of the probability curve in solving problems having two variables. The electrical connection between the battery and the resistors of different value is provided with a male-female connection so that the connectors may be separated and one connected to one of the pins and the other used as a probe in teaching the method of using the probability curve in solving problems.
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