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NDA 2019
Exam
NDA
Year
2019
Subject
Mathematics
Chapter
Basics of Mathematics

NDA 2019 · Mathematics · Basics of Mathematics

The mean weight of 150 students in a certain class is 60 kg. The...

The mean weight of 150 students in a certain class is 60 kg. The mean weight of boys is 70 kg and that of girls is 55 kg. What are the number of boys and girls respectively in the class?

Options

  1. A75 and 75
  2. B50 and 100
  3. C70 and 80
  4. D100 and 50

Correct answer

B. 50 and 100

Step-by-step solution

Let no. of boys be xx. ∴60=70x+55(150−x)150⇒15x+8250=9000⇒15x=750⇒x=50∴ Boys =50 and girls =100.\begin{aligned} & \therefore \quad 60=\frac{70 x+55(150-x)}{150} \\ & \Rightarrow 15 x+8250=9000 \\ & \Rightarrow 15 x=750 \\ & \Rightarrow x=50 \\ & \therefore \text{ Boys }=50 \text{ and girls }=100 . \end{aligned}
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