Question 254151
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If 4 have both cats and dogs and 20 have cats, then 16 must have a cat but not a dog.  Similarly, if 4 have both and 15 have dogs, then 11 must have dogs but no cats.


So 16 plus 4 plus 11 equals 31 of the 40 students have one or the other or both leaving 9 that have neither.



John
*[tex \LARGE e^{i\pi} + 1 = 0]
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