10 + 11 + 12 + 13 + 14 + 15 + 15 + 16 + 17 + 18 + 19 + 20

= ( 10 + 20 ) + ( 11 + 19 ) + ( 12 + 18 ) + ( 13 + 17 ) + ( 14 + 16 ) + ( 15 + 15 )

= 30 + 30 + 30 + 30 + 30 +30 

= 30 x 6

= 180 .

10+11+12+13+14+15+16+17+18+19+20=165

= (11+19) + (12+18) + (13+17) + (14+16) + (10+15)

= 30 + 30 + 30 + 30 + 25 = 145

A = 10 + (11 + 19) + (12 + 18) + (13 + 17) + (14 + 16) + 15

= 10 + 30 + 30 + 30 + 30 + 15 = 145

1+2+...+9+11+18+19=(1+19)+(2+18)+...+(9+11)=20+20+...+20=20*9=180

=(1+19)+(2+18)+...+(9+11)=20+20+20+20+20+20+20+20+20=20x9=180

Số số hạng là :

19 - 1 + 1 = 19 ( số hạng )

Tổng trên là :

( 1 + 19 ) x 19 : 2 = 190

Vậy tổng trên là : 190

Click mik , mik click lại !!!!!!!!!!!!!!!!!!!!!!!!

Tổng hai số là : 

  (1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)=180

         Đáp số : 180

11-12+13-14+15-16+17-18+19-20 = -5

kết quả trên =-5

ok

=210 k nha

turbo pascal là ra ngay

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21=231

trả lời:

=231

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= 1+(2-3)+(4-5)+(6-7)+........+(18-19)+20

= 1+(-1)+(-1)+(-1)+........+(-1)+20

= 1+(-9)+20

= 12

Tính: 1+2-3+4-5+6-7+8-9+10-11+12-13+14-15+16-17+18-19+20 = ?

= 1+(2-3)+(4-5)+(6-7)+........+(18-19)+20

= 1+(-1)+(-1)+(-1)+........+(-1)+20

= 1+(-9)+20

= 12

nhé !