9 thoughts on “To Permute or to Combine?

  1. In the third question , we have not been informed whether the treasurer and the president need to be different people? Cant they both be same? In that case we may have 15*15 ways.
    Is there something which I am missing? Pls help.

    • Common sense: you would not usually vest so much power in a single person (not if they are elected posts…in a dictatorship it would be different of course) so we would assume the default to be “different people” 🙂

      In PnC questions, the wording often admits of more than one interpretation. In such cases I recommend “bhavnaon ko samjho” i.e. try to understand what is the most likely intent of the question-setter. It works more often than you might expect…


  2. Hello J,

    I am not able to understand the 1st question. Marbles are of different colors. Than it should be permutations.
    Please clarify

    • But all marbles of one colour are alike. So we need not arrange them AMONG THEMSELVES. It is like when we choose 3 people out of 10, the three don’t become identical (nor do the 7 rejected).


    • No, since 10P6 would be 10C6 *6! and not 8!. That would mean you have already fixed the position of the first two and are only arranging the new 6 people. Think about it! 🙂


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