Shef08 wrote:
Can someone explain me where did I go wrong?
Ways in which 7 people can be arranged: 7!.... (a)
Ways in which all girls are arranged together: 7P5...... (b)
(as all girls are treated as 1)
So a-b: 7!- 7P5
You have negated only the cases where all 3 girls are seated together.
There are still other scenarios where two girls can be seated together. For example BGGBBBG, GBGGBBB, GGBBGBB, etc. These are also not allowed as per our question. No two girls can be seated together.
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