算一算(一年级奥数题及答案)(2)
学而思奥数网(原创)
2010-12-23 17:49:24
1-2+3-4+5-6+7-8+9-10+11
=1+3-2+5-4+7-6+9-8+11-10
=1+(3-2)+(5-4)+(7-6)+(9-8)+(11-10)
=1+1+1+1+1+1
=6

