if n(s)=36,5/12,find n(A)
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Answer:
As we know,
n
P
r
=
(n−r)!
n!
n−1
P
3
:
n+1
P
3
=5:12
⇒
(n−2)!
(n+1)!
(n−4)!
(n−1)!
=
12
5
⇒
(n+1)n(n−1)
(n−1)(n−2)(n−3)
=
12
5
⇒12(n−2)(n−3)=5(n+1)n
⇒7n
2
−65n+72=0⇒7n
2
−56n−9n+72=0
⇒7n(n−8)−9(n−8)=0⇒(n−8)(7n−9)=0⇒n=8.
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