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Q. $^{15}C_{3} +\,{}^{15}C_{5} + .. ...+\,{}^{15}C_{15} $ will be equal to

WBJEEWBJEE 2011Permutations and Combinations

Solution:

We know,
${ }^{15} C_{1}+{ }^{15} C_{3}+{ }^{15} C_{5}+\ldots+{ }^{15} C_{15}=2^{15-1}$
$\therefore { }^{15} C_{3}+{ }^{15} C_{5}+\ldots+{ }^{15} C_{15}=2^{14}-15$