ANSWER: There is no feeding mandated for someone who is classified as insane as fasting is not obligatory upon him. 

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ANSWER: No. You can fast any day you want for the sake of fasting and not for any other reason and then you can make as much dua as you want, especially before breaking the fast.

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ANSWER: This is not mandatory but highly recommended.  You can fast only 10th as well.

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