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Mathematics
Problem
The number of ways of selecting 'n' things out of '3n' things of which 'n' are of one kind and alike and 'n' are of second kind and alike and the rest unlike is : (a)
n
2
n
−
1
n 2^{n-1}
n
2
n
−
1
(b)
(
n
−
1
)
2
n
−
1
(n-1) 2^{n-1}
(
n
−
1
)
2
n
−
1
(c)
(
n
+
1
)
2
n
−
1
(n+1) 2^{n-1}
(
n
+
1
)
2
n
−
1
(d)
(
n
+
2
)
2
n
−
1
(n+2) 2^{n-1}
(
n
+
2
)
2
n
−
1
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