计算：899998-799999+89998-79999+8998-7999+898-799+88-79
解：
原式 =(899999-799999-1)+(89999-79999-1)+(8999-7999-1)+
(899-799-1)+(89-79-1)
=100000+10000+1000+100+10-1×5
=111110-5
=111105