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JEE MATHEMATICS MCQ: COMBINATIONS

1 Easy

1 of 1

Application +4 | -1

{\;^n}{C_r} + 2{\;^n}{C_{r - 1}} + {\;^n}{C_{r - 2}}

is equal to

View answer and explanation

Correct option: C

{\;^{n + 2}}{C_r}

Option C (

{\;^{n + 2}}{C_r}

) is correct. This is derived by applying the combination identity

{\;^n}{C_r} + {\;^n}{C_{r - 1}} = {\;^{n + 1}}{C_r}

twice.

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is a member of the committee, is A man has 7 friends. In how many ways he can invite one or more of them for a tea party? If

{\;^{n + 2}}{C_8}:{\;^{n - 2}}{P_4} = \frac{{57}}{{16}}

n