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Permutations Practice Test 1
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© examsnet.com
Question : 12
Total: 40
If
9
P
5
+
5
.
9
P
4
=
10
P
r
, then
r
=
?
4
5
9
10
Validate
Solution:
👈: Video Solution
From the given relation,
9
!
4
!
+
5
.
9
!
5
!
=
10
!
(
10
−
r
)
!
⇒
2
4
×
9
!
=
10
×
9
!
(
10
−
r
)
!
⇒
(
10
−
r
)
!
=
5
.
4
!
=
5
!
⇒
10
−
r
=
5
⇒
r
=
5
.
© examsnet.com
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