a.11/7.8/13+8/13.3/7+8/13

=8/13.(11/7+3/7+1)

=8/13.3

=24/13

b.5/7.8/13+8/13.9/7-8/13

=8/13.(5/7+9/7-1)

=8/13.1

=8/13

c.157.199-56.199-199

=199.(157-56-1)

=199.100

19900

a, 7 - x = 8 -(-7)

7-x = 15

x = 7 - 15 = -8

b, x - 8 = (-3) - 8

=> x = -3 ( bỏ đi 8 ở hai vế )

A)\(\left(4-\frac{8}{3}\right)x\frac{15}{7}-\frac{8}{5}:\frac{1}{10}\)

\(=\frac{4}{3}x\frac{15}{7}-\frac{8}{5}x\frac{1}{10}\)
\(=\frac{20}{7}-\frac{4}{25}\)
\(=\frac{222}{185}\)
B)\(\frac{7}{5}x\frac{3}{8}+\frac{7}{5}x\frac{5}{8}-\frac{37}{5}\)
\(=\frac{7}{5}x\left(\frac{3}{8}+\frac{5}{8}\right)-\frac{37}{5}\)
\(=\frac{7}{5}x1-\frac{37}{5}\)
\(=\frac{7}{5}-\frac{37}{5}\)
\(=\frac{-30}{5} \)
\(=-6\)

A =\(\left(4-\frac{8}{3}\right).\frac{15}{7}-\frac{8}{5}:\frac{1}{10}\)

\(=\frac{4}{3}.\frac{15}{7}-16\)

\(=\frac{20}{7}-\frac{112}{7}\)

\(=\frac{-92}{7}\)

B\(=\frac{7}{5}.\frac{3}{8}+\frac{7}{5}.\frac{5}{8}-\frac{37}{5}\)

\(=\frac{7}{5}.\left(\frac{3}{8}+\frac{5}{8}\right)-\frac{37}{5}\)

\(=\frac{7}{5}-\frac{37}{5}\)

\(=-6\)

a)

160 : (4 × 8) = 160 : 32 = 5

160 : 4 : 8 = 40 : 8 = 5

Vậy 160 : (4 × 8) = 160 : 4 : 8.

96 : (3 × 8) = 96 : 24 = 4

96 : 3 : 8 = 32 : 8 = 4

Vậy 96 : (3 × 8) = 96 : 3 : 8.

105 : (5 × 7) = 105 : 35 = 3

105 : 5 : 7 = 21 : 7 = 3

Vậy 105 : (5 × 7) = 105 : 5 : 7.

Nhận xét: a : (b × c) = a : b : c

b)

270 : (9 × 6) = 270 : 9 : 6 = 30 : 6 = 5

420 : (7 × 3) = 420 : 7 : 3 = 60 : 3 = 20

144 : (2 × 8) = 144 : 2 : 8 = 72 : 8 = 9

a,\(\frac{6\times7\times8}{8\times9\times10}=\frac{6\times7}{9\times10}=\frac{7}{15}\)

\(\frac{7}{8}.\frac{9}{11}.\frac{8}{3}:\frac{2}{9}\)

\(=\frac{7.9.8.9}{8.11.3.2}\)

\(=\frac{189}{11}\)

Dấu \(\left(.\right)\)là dấu nhân nhé

\(\frac{6\times7\times8}{8\times9\times10}\)

\(=\frac{6\times7}{9\times10}\)

\(=\frac{42}{90}=\frac{7}{15}\)

7 - x = 8 - ( -7 ) 

7 - x = 1 

     x = 7 - 1 

     x = 6 

x - 8 = ( -3 ) - 8 

x - 8 = 5 

x      = 5 + 8 

x      = 13 

a) 7 - x = 8 - (-7) 

    7 - x = 15

         x = 7 - 15

         x = - 8

b) x - 8 = (-3) - 8.

    x - 8 = (-11)

    x      =(-11) + 8

    x      = - 3

a) Thiếu đề

b) ` 4/7 xx 8/13 + 8/13 xx 3/7`

= ` 8/13 xx ( 4/7 + 3/7)`

` = 8/13 xx 7/7`

` = 8/13 xx 1`

` = 8/13`

a) thiếu đề

b) \(=\left(\dfrac{4}{7}+\dfrac{3}{7}\right)\times\dfrac{8}{13}\\ =1\times\dfrac{8}{13}=\dfrac{8}{13}\)