1.

The value of `sum_(r=0)^(10)r""^(10)C_(r)3^(r)(-2)^(10-r)` isA. 20B. 10C. 300D. 30

Answer» Correct Answer - D
`underset(r=0)overset(10)sumr^(10)C_(r)3^(r)(-2)^(10-r)= 10 underset(r=0)overset(10)sum.^(9)C_(r-1)3^(r)(-2)^(10-r)`
`= 10 xx 3 underset(r=0)overset(10)sum.^(9)C_(r-1)3^(r-1)(-2)^(10-r)`
`= 30(3-2)^(9) = 30`


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