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put this solution on YOUR website! A proportion means two ratios are equal.  The ratio is student pet owners to students.
3 out of 5 is the ratio 3/5.  6 out of 11 is 6/11.  Set them equal, then cross multiply.  If the products are the same, then the ratios are equal and thus proportional.
3/5 = 6/11 --> 33 = 30?  No.  The ratios are not proportional.