设女生原来有x人,则男生原来有570-x人.
4/5x+(570-x)*6/7=610
5/4x+570*6/7-6/7x=610
5/4x+665-6/7x=610
665-(6/7x-5/4x)=610
665-(30/35x-30/11x)=610
665-30/11x=610
665-610=30/11x
55=33/11x
x=55*11/30
x=150
570-x=570-150=420
420-150=270
答：多270人.