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The mean marks of boys and girls in an exam are 70 and 73.if mean marks of whole class is 71 find ratio of number of girls to number of boys



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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)
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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