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Given: David and Rachel are getting married. The extended family wants to have its picture taken, but David's father is unwilling to stand next to Rachel's mother. Asked: How many options does the photographer have to arrange the 10 family members in a row for the picture?

Number of options the photographer have to arrange the 10 family members in a row for the picture without any condition = 10!
Number of ways in which David's father is standing next to Rachel's mother = 2 * 9!
Number of options the photographer have to arrange the 10 family members in a row for the picture in which David's father is not standing next to Rachel's mother = 10! - 2*9! = 9! (10-2) = 8*9!

IMO C
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otal number of possible arrangements - Arrangement where David's father stands next to R's mother = Arrangement possible where David's father doesn't stand next to R's mother.
Total arrangements possible = 10!
Arrangement where D's father stands next to R's mother = 9! * 2
So, 10! - 9!*2
= 9!(10 - 2)
=9! * 8 (C), IMO
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