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Question

The mean weight of 150 students in a certain class is 60 kilograms. The mean weight of boys in the class is 70 kilograms and that of the girls is 55 kilograms, then the number of boys and girls are,


A

100,50

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B

50,100

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C

75,75

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D

60,90

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Solution

The correct option is B

50,100


The explanation for the correct option:

Given that total student in the class is 150 and the mean weight is 60kg.

Totalweight=150×60=9000kg

Let us consider the total number of boys be x and given that the mean weight of boys is70kg.

Totalweightofboys=70×x=70xkg

Totalnumberofgirls=Totalstudents-numberofboys=150-x

Since the mean weight of girls is 55kg.

Totalweightofgirls=55×(150x)=(55×150)-55x=(8250-55x)kg

Totalweight=weightofboys+weightofgirls9000=70x+(8250-55x)9000=70x+8250-55x9000-8250=70x55x750=15xx=75015x=50

So, the number of boys =50

Numberofgirls=150-50=100

Hence, the correct option is B.


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