1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+19+20/20
1 câu trả lời
= 1 + 2 + 3 + .... + 18 + 19 + 1
= ( 1 + 19 ) + ( 2 + 18 ) + ( 3 + 17 ) +.... + ( 10 + 1 )
= 20 + 20 + 20 +... + 11
= (20 × 9) + 11
= 191
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+19+20/20
= 1 + 2 + 3 + .... + 18 + 19 + 1
= ( 1 + 19 ) + ( 2 + 18 ) + ( 3 + 17 ) +.... + ( 10 + 1 )
= 20 + 20 + 20 +... + 11
= (20 × 9) + 11
= 191
