The mean weight of $20$ students is $25$ kg and the mean weight of another $10$ students is $40$ kg. Find the mean weight of the $30$ students.

20

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30

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40

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50

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Solution

The correct option is C $30$
$Given Mean weight of 20 students = 25 \Rightarrow \frac{Sum of weight of 20 students}{20} = 25 \Rightarrow Sum of weight of 20 students = 25 \times 20 = 500 k g Given Mean weight of 10 students = 40 \Rightarrow \frac{Sum of weight of 10 students}{10} = 40 \Rightarrow Sum of weight of 10 students = 40 \times 10 = 400 k g$
Mean weight of all 30 students
$\Rightarrow \frac{Sum of weight of 30 students}{30} \Rightarrow \frac{Sum of weight of 20 students+Sum of weight of 10 students}{30} = \frac{500 + 400}{30} = \frac{900}{30} = 30 k g$

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