Question

[Nguyễn Trang]

Tính nhanh:

S=1-2-3+4+5-6-7+.....+97-98-99+100

Answer 1

[Trần_Hiền_Mai]

S=1-2-3+4+5-6-7+...+97-98-99+100

  =(1-2-3)+4+(5-6-7)+8...+(97-98-99)+100

  =(-4)+4+(-8)+8+...+(-100)+100

  =[(-4)+4]+[(-8)+8]+...+[(-100)+100]

  =0+0+...+0

  =0