Mình nghĩ đề là : 2/8 sẽ hay hơn.

\(B=\dfrac{5}{2}+\dfrac{6}{11}+\dfrac{2}{8}+\dfrac{7}{2}+\dfrac{6}{8}+\dfrac{5}{11}\)

\(=\left(\dfrac{5}{2}+\dfrac{7}{2}\right)+\left(\dfrac{6}{11}+\dfrac{5}{11}\right)+\left(\dfrac{2}{8}+\dfrac{6}{8}\right)\)

\(=6+1+1=8\)

\(B=\dfrac{5}{2}+\dfrac{6}{11}+\dfrac{3}{8}+\dfrac{7}{2}+\dfrac{6}{8}+\dfrac{5}{11}\)

\(B=\left(\dfrac{5}{2}+\dfrac{7}{2}\right)+\left(\dfrac{6}{11}+\dfrac{5}{11}\right)+\left(\dfrac{3}{8}+\dfrac{6}{8}\right)\)

\(B=6+1+1,125\)

\(B=8,125\)

a) 2/5 x 1/4 + 3/4 x 2/5
 = 2/5 x (1/4 + 3/4)
 = 2/5 x        1
 =      2/5
b) 6/11 : 2/3 + 5/11 : 2/3
 = (6/11 + 5/11) : 2/3
 =         1           : 2/3
 =               3/2

\(a,A=\dfrac{\dfrac{5}{4}+\dfrac{5}{5}+\dfrac{5}{7}-\dfrac{5}{11}}{\dfrac{10}{4}+\dfrac{10}{5}+\dfrac{10}{7}-\dfrac{10}{11}}\\ =\dfrac{5.\left(\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{1}{7}-\dfrac{1}{11}\right)}{10.\left(\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{1}{7}-\dfrac{1}{11}\right)}\\ =\dfrac{5}{10}\\ =\dfrac{1}{2}\)

Vậy \(A=\dfrac{1}{2}\)

\(b,B=\dfrac{2+\dfrac{6}{5}-\dfrac{6}{7}-\dfrac{6}{11}}{\dfrac{2}{3}+\dfrac{2}{5}-\dfrac{2}{7}-\dfrac{2}{11}}\\ =\dfrac{3.\left(\dfrac{2}{3}+\dfrac{2}{5}-\dfrac{2}{7}-\dfrac{2}{11}\right)}{\dfrac{2}{3}+\dfrac{2}{5}-\dfrac{2}{7}-\dfrac{2}{11}}\\ =3\)

Vậy \(B=3\)

=6/11x(3/5+2/5)

=6/11x1

=6/11

hok tốt

....................

nhận thấy có 6/11 chung

 =6/11*(3/5+2/5)

=6/11*(1)

=6/11

coi lại câu a

1.1+1.1+1.1+1.1+1.1/1.1+1.1+9.3+6.8+.2

bằng 3845/429

Đ/S là 3845/429

Đặt \(A=\frac{3}{5}+\frac{6}{11}+\frac{7}{11}+\frac{2}{5}+\frac{16}{11}+\frac{19}{13}\)

\(A=\left(\frac{3}{5}+\frac{2}{5}\right)+\left(\frac{6}{11}+\frac{7}{11}+\frac{16}{11}\right)+\frac{19}{13}\)

\(A=1+\frac{29}{11}+\frac{19}{13}\)

\(A=\frac{11}{11}+\frac{29}{11}+\frac{19}{13}=\frac{40}{11}+\frac{19}{13}=\frac{729}{143}\)

@Phạm Thị Mai Anh , @ngân sai kết quả với lại không có lời giải :v

1+2+3+4+5+6+7+8+9+10+11+12+13-1-2-3-4-5-6-7-8-9-10-11-12

=(1-1)+(2-2)+(3-3)+(4-4)+(5-5)+(6-6)+(7-7)+(8-8)+(9-9)+(10-10)+(11-11)+(12-12)+13

=  0  +  0  +  0  +  0  +   0  +  0  +  0  +  0  +  0  + 0  + 0   +  0  +  13

=                                 13

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 - 1 - 2 - 3 - 4 - 5 - 6 - 7- 8 - 9 - 10 

= (1+12) + (2+11) + (3+10) + ( 4+9) + (5+8) + (6+7) + 13 -  (1+11) - ( 2+10) - ( 3+9) - (4+8) - (5+7) + 6 + 12

= 13 * 7 - 12 * 6 + 6

= 13

Ai k mk mk k lại

= 13 nhé hihi nha