Question 185508




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An essential number is missing in your post.
However, Clara should be expected to be right in her 
selections (1/4)th of the time or (1/4)x, where x
is the number of cards you ask her to identify.
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The standard deviation is sqrt[x(1/4)(3/4)]
= (1/4)sqrt(3x)
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Cheers,
Stan H.