A) 30
B) 50
C) 70
D) 90
Correct Answer: B
Solution :
(b): \[\sum\limits_{1}^{n}{\left( {{x}_{i}}+5 \right)=\sum\limits_{1}^{n}{{{x}_{i}}+5n=200}}\]???(1) \[\sum\limits_{i=1}^{n}{\left( {{x}_{i}}+9 \right)=\sum\limits_{1}^{n}{{{x}_{i}}+9n=400}}\]?????(2) Subtracting (2) ? (1) \[\Rightarrow \]4n = 200 \[\Rightarrow \]n = 50
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