= 13/30

Lời giải:

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

$=\frac{5}{5}+\frac{22}{11}=\frac{26}{13}=1+2+2=5$

A =\(\frac{7}{19}.\frac{8}{11}+\frac{7}{19}.\frac{3}{11}+\frac{12}{19}\)

A = \(\frac{7}{19}.\left(\frac{8}{11}+\frac{3}{11}\right)\)+ \(\frac{12}{19}\)

A = \(\frac{7}{19}.1+\frac{12}{19}\)

A = \(\frac{7}{19}+\frac{12}{19}\)

A = 1

--------

B = \(\frac{5}{9}.\frac{7}{13}+\frac{5}{9}.\frac{9}{13}-\frac{5}{9}.\frac{3}{13}\)

B = \(\frac{5}{9}.\left(\frac{7}{13}+\frac{9}{13}-\frac{3}{13}\right)\)

B = \(\frac{5}{9}.1\)

B = \(\frac{5}{9}\)

-------

C = \(\left(\frac{67}{111}+\frac{2}{33}-\frac{15}{117}\right).\left(\frac{1}{3}-\frac{1}{4}-\frac{1}{12}\right)\)

C = \(\left(\frac{67}{111}+\frac{2}{33}-\frac{15}{117}\right).\left(\frac{4}{12}-\frac{3}{12}-\frac{1}{12}\right)\)

C = \(\left(\frac{67}{111}+\frac{2}{33}-\frac{15}{117}\right).0\)

C = 0

Chúc bạn học tốt

Gợi ý: Sử dụng tính chất phân phối của phép nhân đối với phép cộng để nhóm thừa số chung ra ngoài.

A=\(\frac{6}{19}\). \(\frac{-7}{11}\)+\(\frac{6}{19}\).\(\frac{-4}{11}\)+\(\frac{-13}{19}\)

  =\(\frac{6}{19}\).(\(\frac{-7}{11}\)+\(\frac{-4}{11}\))+\(\frac{-13}{19}\)

 =\(\frac{6}{19}\).\(\frac{-11}{11}\)+\(\frac{-13}{19}\)

  =\(\frac{6}{19}\).-1 +\(\frac{-13}{19}\)

=\(\frac{-6}{19}\)+\(\frac{-13}{19}\)

=\(\frac{-19}{19}\)

+1

=1  nhầm

a) Cách 1: Thay x = 7, ta có:

(23 + x) - (56 - x)

= (23 + 7) - (56 - 7)

= 30 - 49

= -19

Cách 2: 

Thay x = 7, ta có:

(23 + x) - (56 - x)

= (23 + 7) - (56 - 7)

= 23 + 7 - 56 + 7

= 30 - 56 + 7

= (-26) + 7

=-19.

b)  Cách 1: Thay x = 13, y = 11, ta có:

25 - x - (29 + y - 8)

= 25 - 13 - (29 + 11 - 8)

= 12 - 32

= -20.

Cách 2: Thay x = 13, y = 11, ta có:

25 - x - (29 + y - 8)

= 25 - 13 - (29 + 11 - 8)

= 25 - 13 - 29 - 11 + 8

= 12 - 29 - 11 + 8

= (-17) - 11 + 8

= (-28) + 8

=-20.

\(\frac{3}{5}+\frac{5}{1}+\frac{7}{13}\)\(+\frac{2}{5}+\frac{16}{11}+\frac{19}{13}\)

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

=1+2+5+\(\frac{16}{11}\)

=...

3/5 + 5/1 + 7/13 + 2/5 +16 /11+19/13

= (3/5+2/5)+(5/1+16/11)+(7/13+19/13)

=1+21/11+28/13

bạn tự tính tiếp nhé tiếp theo dễ lắm

a) 5

b) 11/6

\(A=\dfrac{7}{19}\cdot\dfrac{8}{11}+\dfrac{7}{11}\cdot\dfrac{3}{11}\\ =\dfrac{7\cdot8}{19\cdot11}+\dfrac{7}{11}\cdot\dfrac{3}{11}\\ =\dfrac{8}{19}\cdot\dfrac{7}{11}+\dfrac{7}{11}\cdot\dfrac{3}{11}\\ =\dfrac{7}{11}\cdot\left(\dfrac{8}{19}+\dfrac{3}{11}\right)\\ =\dfrac{7}{11}\cdot\dfrac{145}{209}\\ =\dfrac{1015}{2299}\)

= \(\dfrac{7}{19}\) . \(\dfrac{8}{11}\) + \(\dfrac{7}{11}\) . \(\dfrac{3}{11}\)

= \(\dfrac{56}{209}\) + \(\dfrac{21}{121}\)

= \(\dfrac{1015}{2299}\)

Cách 1 : \(A=\dfrac{7}{19}.\dfrac{8}{11}+\dfrac{7}{11}.\dfrac{3}{11}\)

= \(\dfrac{7.8}{19.11}+\dfrac{7}{11}.\dfrac{3}{11}\)

= \(\dfrac{8}{19}.\dfrac{7}{11}+\dfrac{7}{11}.\dfrac{3}{11}\)

= \(\dfrac{7}{11}.\left(\dfrac{8}{19}+\dfrac{3}{11}\right)\)

= \(\dfrac{7}{11}.\dfrac{145}{209}\)

= \(\dfrac{1015}{2299}\)

Cách 2 : \(A=\dfrac{7}{19}.\dfrac{8}{11}+\dfrac{7}{11}.\dfrac{3}{11}\)

= \(\dfrac{56}{209}+\dfrac{21}{121}\)

= \(\dfrac{1015}{2299}\)

~~~~~~~~<<Chúc bạn học tốt>>~~~~~~~~

11 + 12 + 3 + 4 + 5 + 6 + 7 + 18 + 19 + 10

= ( 11 + 19 ) + ( 12 + 18 ) + ( 3 + 7 ) + ( 4 + 6) + 5 + 10

= 30 + 30 + 10 + 10 + 5 + 10

= 95

Vậy đáp án cần chọn là D