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6.Permutation and Combination
easy
જો $^{15}{C_{3r}}{ = ^{15}}{C_{r + 3}}$ ,તો $r$ ની કિંમત મેળવો.
A
$3$
B
$4$
C
$5$
D
$8$
(IIT-1967)
Solution
(a) $^{15}{C_{3r}}{ = ^{15}}{C_{r + 3}}{ \Rightarrow ^{15}}{C_{15 – 3r}}{ = ^{15}}{C_{r + 3}}$
$ \Rightarrow 15 – 3r = r + 3 $
$\Rightarrow r = 3$.
Standard 11
Mathematics