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What is the difference between :-

  1. $5$ boys and $5$ girls need to sit in a row so that no two boys should sit together
  2. $5$ boys and $5$ girls should sit in a row alternatively ?
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condition $2$ is a $subset$ of possibilities of condition $1$. – Suraj M S Dec 6 '13 at 6:49
Alternatively is incorrect; the correct word here is alternately. – Brian M. Scott Dec 6 '13 at 20:36
Yea Mr.Brian M.Scott sorry for the spelling mistake. – user3065912 Dec 10 '13 at 5:54

BGBGBGBGGB is allowed for the first one but not for the second one.

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At the first one you are looking just at the boys, you need to verify that there are no two boys siting together. What about the girls? you don't mind...

At the second part you have to make sure that all the boys and the girls are not siting together...

Hope it's clear :-)

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