descazut-scazator=rest (diferenta)
descazut=rest+scazator
descazut+scazator+rest=640 inlocuiesc si vom avea
rest+scazator+rest+scazator=640
2x(rest+scazator)=640
rest+scazator=640/2
rest+scazator=320
acum descazut=rest+scazator, dar rest+scazator=320 resulta descazut=320