# To Permute or to Combine?

## 9 thoughts on “To Permute or to Combine?”

1. ramarjun |

hello..!!
in the last ques…why cant we say person 1 can slap rest 7….
person 2…rest 7… & so on..
thus total slaps = 7^8

• You are multiplying instead of adding. If you add you will get the same answer 7 + 7 + 7 +…+ 7 = 56.

regards
J

2. chess player |

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” ðŸ™‚

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…

regards
J

• chess player |

got it, thanks.This blog is excellent.

3. Parthp |

Hello J,

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

• 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).

regards
J

4. sayani |

Hello J ,
Wouldn’t it be the same in case of the rowing question ? 10p6 or 10c6*8! ? Please help.

• 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! ðŸ™‚

regards
J