# The order in which the musicians perform is completely determined if which one of the following is true?

on July 6, 2020

Why can't the answer be C?

If N is 4th doesn't that mean L has to be 1 and p has to be 7 so we can place all the other letters accordingly

Shunhe on July 7, 2020

Hi @Omar.Elgohail,

Thanks for the question! So remember, we’re looking for an answer choice that will allow us to completely determine the order in which the musicians perform, no ambiguities whatsoever. So let’s say that N plays 4th. Well, if N plays 4th, then we know that MTP will go in slots 5, 6, and 7. Since P can’t be in first, because then M would be in 3rd, and then L would have to go in 2nd, and then we wouldn’t have anywhere to put O. So P has to be in 7th, and then M has to be in 5th, and T has to be in sixth. So right now we know for sure

__ __ __ N M T P

So now the question becomes, can we completely determine the order of the first three? And the answer is no. It’s actually not true that L has to be 1; it’s only true that P has to be 7. We know that S has to be in slot 2, since L and O have be be separated by one. So

__ S __ N M T P ?
But we do know which of L and O go first? No, we just know that there’s a performance between L and O, but not which one goes first, and none of the other rules helps us determine this. So (C) gets us two possibilities

O S L N M T P
L S O N M T P

And so since we need an answer that only leaves one possibility, (C) isn’t it.

Hope this helps! Feel free to ask any other questions that you might have.