设原价出售x本．18x+ 2 3 x×（18-10）=2870 18x+ 16 3 x=2870 70 3 x÷ 70 3 =2870÷ 70 3 x=123123+123× 2 3 =123+82=205（本）答：书店里卖出这种挂历205本．
