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Byju's Answer
Standard XII
Mathematics
nCr Definitions and Properties
If nPr= 360...
Question
If
n
P
r
=
360
and
n
C
r
=
15
then find the value of r
A
5
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B
4
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C
3
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D
2
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Solution
The correct option is
D
4
n
P
r
=
n
!
(
n
−
r
)
!
=
360
-- (1)
n
C
r
=
n
!
(
r
!
)
(
n
−
r
)
!
=
15
-- (2)
Dividing eqn 1 by 2, we get
=
>
r
!
=
360
15
=
24
=
>
r
!
=
4
×
2
×
3
×
1
=
4
!
So,
r
=
4
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1
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