Mean weight of 150 students in a class is 60 ,kg. mean weight of boys is 70, kg and that of girls is

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The mean weight of $150$ students in a class is $60 \,kg.$ The mean weight of boys is $70\, kg$ and that of girls is $55 \,kg$. What is the number of boys in the class?

A

$50$

B

$60$

C

$75$

D

$100$

Solution

Let the no of boys in a class $=x$

$\therefore x \times 70+(150-x) 55=150 \times 60$

$70 x-55 x=9000-8250 \Rightarrow 15 x=750$

$x=50 \Rightarrow$ No. of boys $=50$

Standard 13

Quantitative Aptitude

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