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2016-02-26T23:51:10+05:30

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Let the number of boys be x
and the number of girls be y
mean= (sum of marks obtained by all)/(total number of students)
A/q,
for boys,
70 = (total marks obtained by boys)/x
⇒total marks obtained by boys= 70x
for girls,
73=(total marks obtained by girls)/y
⇒total marks obtained by girls = 73y
for whole class,
71= (total marks obtained by all)/(x +y)
⇒total marks obtained by all = 71(x +y)
⇒70x +73y = 71x + 71y
⇒71x - 70x = 73y - 71y
⇒x =2y
⇒y/x = 1/2
⇒y:x = 1:2

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