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The mean weight of 150 students in a certain class is 60 Kg. The mean weight of the boys from the class is 70 kg, while that of girls is 55 kg. What is the number of girls in the class?

A) 105
B) 100
C) 95
D) 60

Correct Answer:


B) 100

Description for Correct answer:
The mean weight of 150 students is 60 kg

Therefore, Total weight of 150 students = \( \Large \left(150 \times 60\right) Kg = 9000 Kg \)

Now, mean weight of all boys from the class is 70 kg and mean weight of all girls from the class is 55 kg.

Let the number of girls be x, then number of boys be (150 - x)

Therefore, Total weight of class = weight of all boys + weight of all girls

\( \Large 9000 = \left(150 - x\right) \times 70 + 55x \)

\( \Large 9000 = 10500 - 70x + 55x \)

\( \Large 15x = 10500 - 9000 \)

\( \Large 15x = 1500 \)

x = 100

Total number of girls in the class are 100.

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