Q1 of 8 Page 293

The mean weight of 150 students in a class is 60 kg. The mean weight of boys is 70 kg while that of girls is 55 kg. Find the number of boys and girls.

Let the number of boys is ‘x' and the number of girls is (150 – x)


Mean weight of 150 students = 60 kg


Mean weight of ‘x’ boys = 70kg


Total weight of boys = 70x


Mean weight of (150 – x) girls = 55


Total weight of girls = (150 – x) × 55



Applying above formula,




70 x – 55 x + 150 × 55 = 150 × 60


15 x + 8250 = 9000


15 x = 750



x = 50


So, the number of boys 50 and number of girls 150 – 50 = 100


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