Ta có

2/9=6/27

1/3=9/27

Vì 5/27<6/27<9/27 nên 5/27<2/9<1/3

Nên đội thứ hai làm được nhieuf nhất,đội thứ ba làm được ít nhất.

b)Nếu làm chung thì mỗi giờ cả ba đội làm được là :

2/9+1/3+5/27=6/27+9/27+5/27=20/27(công việc ).

a) \(x-\frac{2}{3}=\frac{- 5}{12};x=-\frac{-5}{12}+\frac23;x=\frac14\)

b) \(\frac{8}{5}:x=\frac{- 2}{3};\frac85:x=-\frac23;\frac85\frac{.1}{x}=-\frac23;\frac{8}{5x}=-\frac23;24=-10x;-10x=24;x=-\frac{12}{5};x=-\frac{12}{5}\)

c) \(1-\frac{3}{7}.x=-\frac{2}{7};7-3x=-2;-3x=-7-2;-3x=-9;x=-\frac{9}{-3}=3;x=3\)

a)-2/7+2/7:3/5

-2/7+(2/7:3/5)

-2/7+10/21

42/147+70/147

102/147

b)-8/19+-4/21-17/21+27/19

(8/19+27/19)-(-4/21+17/21)

35/19-1

35/19

c)6/5 . 3/13-6/5 . 16/13

18/65-6/5 . 16/13

18/65-96.65

-6/5

a)-2/7+2/7:3/5

-2/7+(2/7:3/5)

-2/7+10/21

42/147+70/147

102/147

b)-8/19+-4/21-17/21+27/19

(8/19+27/19)-(-4/21+17/21)

35/19-1

35/19

c)6/5 . 3/13-6/5 . 16/13

18/65-6/5 . 16/13

18/65-96.65

-6/5

a)-2/7+2/7:3/5

-2/7+(2/7:3/5)

-2/7+10/21

42/147+70/147

102/147

b)-8/19+-4/21-17/21+27/19

(8/19+27/19)-(-4/21+17/21)

35/19-1

35/19

c)6/5 . 3/13-6/5 . 16/13

18/65-6/5 . 16/13

18/65-96.65

-6/5

a)-2/7+2/7:3/5

-2/7+(2/7:3/5)

-2/7+10/21

42/147+70/147

102/147

b)-8/19+-4/21-17/21+27/19

(8/19+27/19)-(-4/21+17/21)

35/19-1

35/19

c)6/5 . 3/13-6/5 . 16/13

18/65-6/5 . 16/13

18/65-96.65

-6/5

a)-2/7+2/7:3/5

-2/7+(2/7:3/5)

-2/7+10/21

42/147+70/147

102/147

b)-8/19+-4/21-17/21+27/19

(8/19+27/19)-(-4/21+17/21)

35/19-1

35/19

c)6/5 . 3/13-6/5 . 16/13

18/65-6/5 . 16/13

18/65-96.65

-6/5

a)-2/7+2/7:3/5

-2/7+(2/7:3/5)

-2/7+10/21

42/147+70/147

102/147

b)-8/19+-4/21-17/21+27/19

(8/19+27/19)-(-4/21+17/21)

35/19-1

35/19

c)6/5 . 3/13-6/5 . 16/13

18/65-6/5 . 16/13

18/65-96.65

-6/5

a)-2/7+2/7:3/5

-2/7+(2/7:3/5)

-2/7+10/21

42/147+70/147

102/147

b)-8/19+-4/21-17/21+27/19

(8/19+27/19)-(-4/21+17/21)

35/19-1

35/19

c)6/5 . 3/13-6/5 . 16/13

18/65-6/5 . 16/13

18/65-96.65

-6/5

a) \(\frac{- 2}{7}+\frac{2}{7}:\frac{3}{5}=-\frac27+\left(\frac27.\frac53\right)=-\frac27+\frac{10}{21}=-\frac{14}{21}+\frac{10}{21}=\frac{-4}{21}\)

b) \(\frac{- 8}{19}+\frac{- 4}{21}-\frac{17}{21}+\frac{27}{19}=\left(-\frac{8}{19}+\frac{27}{19}\right)+\left(-\frac{4}{21}+\frac{-17}{21}\right)=\frac{19}{19}+\frac{-21}{21}=1-1=0\)

c) \(\frac{6}{5}.\frac{3}{13}-\frac{6}{5}.\frac{16}{13}=\frac65^{}.\left(\frac{3}{13}-\frac{16}{13}\right)=\frac65.\frac{-13}{13}=-\frac65.1=-\frac65\)