E
Editor
Sep 18, 2022
$^{n}C_{r}+2^{n}C_{r-1}+^{n}C_{r-2}$=
Difficulty: Easy
A:
$^{n+1}C_{r}$
B:
$^{n-1}C_{r}$
C:
$^{n+2}C_{r}$
D:
$^{n-2}C_{r-1}$
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ID: 63273dbaca83163ac3a12491