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2015-02-01T15:34:23+05:30

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Let the number of boys = x
number of girls = y
we need to find  \frac{x}{y} .

The average score of boys in the examination is 71
total score of boys = 71 
× x = 71x
The average score of girls in the examination is 73
total score of girls = 73 
× y = 73y
So total mark of school = 71x + 73y     ---------------(1)

average score if school in examination 71.8
so total mark = 71.8 
× (x+y)             -----------------(2)

From equations (1) and (2);
 
71x + 73y = 71.8(x+y)
⇒ 71x + 73y = 71.8x + 71.8y
⇒ 73y - 71.8y = 71.8x - 71x
⇒ 1.2y = 0.8x
⇒0.8x = 1.2y

 \frac{x}{y} = \frac{1.2}{0.8}= \frac{3}{2} =\boxed{3:2}

Ratio of boys and girls is 3:2.
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2015-02-01T15:38:20+05:30
The ratio of number of boys to that of girls appeared in the examination is 3:2.
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