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Question

The mean weight of 120 students in the second year class of a college is 56kg, If the mean weight of the boys and that of the girls in the class are 60kg and 50kg respectively, then the number of boys and girls separately in the class are

A
72,64
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B
38,64
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C
72,48
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D
None of these
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Solution

The correct option is B 72,48
We know that the combined mean A=n1A1+n2A2n1+n2 ...(1)
Here A1= mean weight of boys =60kg
A2= mean weight of girls =50kg
A= combined mean =56kg
and n1+n2=120 ...(2)
So, from (1) and (2)
56=n1.60+n2.5012056×120=n1.60+(120n1)50;120(5650)=10n1n1=72,n2=48
Thus, the number of boys =72 and the number of girls =48.

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