100-99+98-97+96-95+94-93+....+4-3+2-1 =(100-99)+(98-97)+(96-95)+(94-93)+....+(4-3)+(2-1) =1+1+1+……+1 =50
100+99-98-97+96+95-94-93+...+8+7-6-5+4+3-2-1
=(100+99-98-97)+(96+95-94-93)+...+(8+7-6-5)+(4+3-2-1)
=4+4+...+4+4 (计25个)
=100
100+99-98-97+96+95-94-93+......+4+3-2-1
=(100+99-98-97)+(96+95-94-93)+......+(4+3-2-1)
=100÷4X4
=100
=(100-98)+(99-97)+……+(4-2)+(3-1) =2?50=100