A) 20
B) 10
C) 30
D) 300
Correct Answer: C
Solution :
[c] \[\sum\limits_{r=0}^{10}{r\times \left( \frac{10}{r} \right)\times 3\times {{3}^{r-1}}\times {{(-2)}^{10-r}}{{\times }^{9}}{{C}_{r-1}}}\] \[\Rightarrow 10.3\sum\limits_{r=0}^{10}{^{9}{{C}_{r-1}}}{{.3}^{r-1}}\times {{\left( -2 \right)}^{9-(r-1)}}\] \[\Rightarrow 30{{[3-2]}^{10}}=30\times 1=30\]
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