In a class of 'x' students, if 4 boys are replaced with 4 girls, the ratio of the boys to girls in the class becomes 1:2. On the contrary, if 6 girls are replaced with 6 boys, the ratio of boys to girls becomes equal. What is the present percentage of boys in the class?

1) 40
2) 33.33
3) 44.44
4) 37.5

• there are 'x' students in class where 'y' are boys (let say) then girl will be (x-y)/x
  the ratio of boys and girls will be y/(x-y)
  according to condition 1 we may write,
  (y-4)/(x-y+4)=(1/2)
  & according to condition 2 we may write,
  (y+6)/(x-y-6) = (1/1)
  solving these two equation we get, x=60 & y =24
  then the present percentage of boys will be 24*100/60=40%
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