买一送一是打几折? 付1得2 1÷(1+1) =1÷2 =0.5 =五折 买二送三是打几折? 付2得5 2÷(2+3) =2÷5 =0.4 =四折 买三送二是打几折? 付3得5 3÷(2+3) =3÷5 =0.6 =六折 买四送一是打几折? 付4得5 4÷(4+1) =4÷5 =0.8 =八折 买四送三是打几折? 付4得7 4÷(4+3) =4÷7 ≈0.57 =五七折 买七送三是打几折? 付7得10 7÷(7+3) =7÷10 =0.7 =七折