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6.Permutation and Combination
normal
If $n$ is even and the value of $^n{C_r}$ is maximum, then $r = $
A
$\frac{n}{2}$
B
$\frac{{n + 1}}{2}$
C
$\frac{{n - 1}}{2}$
D
None of these
Solution
The binomial coefficient series is
${ }^n C_0,{ }^n C_1,{ }^n C_2, \ldots,{ }^n C r, \ldots .,{ }^n C_{n-2},{ }^n C_{n-1},{ }^n C_n$
the task is to find maximum value of ${ }^{ n } Cr$
The value of coefficients increasing initially and reaches its maximum and then start reducing value in middle is maximum
total term are $=n+1$
${ }^n Cr$ is $r +1$ th term
middle term $=(n+1+1) / 2=n / 2+1$
$r+1=n / 2+1$
$r=n / 2$
If $n$ is even and the value of ${ }^n C r$, is maximum, when $r=n / 2$
if $n$ is odd, the maximum occurs at $r=(n-1) / 2$ and at $r=(n+1) / 2$.
$r=n / 2$ if $n$ is Even
Standard 11
Mathematics