a: =20/90+15/90+54/90=89/90

b: =(9/13+4/13)+2/3=1+2/3=5/3

a, 2/5 + 1/6 + 3/5

= ( 2/5 + 3/5 ) + 1/6

=        5/5 + 1/6

=          1 + 1/6

=         6/6 + 1/6 

=            7/6

b, 9/13 + 4/13 + 2/3

=        13/13    + 2/3

=            1 + 2/3

= 3/3 + 2/3

=             5/3

2/5+1/6+3/5

=(2/5+3/5)+1/6

=5/5+1/6

=1+1/6

=7/6

9/13+4/13+2/3

=(9/13+4/13)+2/3

=13/13+2/3

=1+2/3

=5/3

k mk nha các bạn, nhớ kb mk đó

2/5+1/6+3/5=(2/5+3/5)+1/6

                   =1+1/6=7/6

9/13+4/13+2/3

=(9/13+4/13)+2/3

=1+2/3=5/3

giúp nhanh ạ, mình cần gấp

Bài 5:

a: =1/3+2/5

=5/15+6/15

=11/15

b: =6/21+12/21=18/21=6/7

c: =16/24+10/24

=26/24

=13/12

d: =4/12+3/12+10/12

=17/12

e: =19/24-9/24

=10/24

=5/12

f: =8/9-3/9=5/9

g: =9/3+1/3=10/3

k: =15/24+42/24+14/24

=71/24

mk tưởng bn học lớp 1

kg có cậu trả lời đi

not, mk lười lắm :)

a \(\frac{7}{6}\)

b \(\frac{5}{3}\)

\(a,\frac{2}{5}+\frac{1}{6}+\frac{3}{5}\)

\(=\left(\frac{2}{5}+\frac{3}{5}\right)+\frac{1}{6}\)

\(=1+\frac{1}{6}\)

\(=\frac{7}{6}\)

Hok tốt!~

\(\frac{2}{5}+\frac{1}{6}+\frac{3}{5}\)

\(=\frac{2}{5}+\frac{3}{5}+\frac{1}{6}\)

\(=\frac{5}{5}+\frac{1}{6}\)

\(=1+\frac{1}{6}\)

\(=1\frac{1}{6}=\frac{7}{6}\)

A  =\(\frac{2}{5}\times\frac{4}{7}+\frac{3}{5}\times\frac{4}{7}\)  B = \(\frac{17}{13}\times\frac{12}{17}-\frac{4}{13}\times\frac{12}{17}\)   C = \(\frac{9}{14}:\frac{6}{7}+\frac{5}{14}:\frac{6}{7}\)  D =\(\frac{9}{12}:\frac{7}{9}\times\frac{12}{19}\)

=  \(\frac{4}{7}\times\left(\frac{2}{5}+\frac{3}{5}\right)\)              =\(\left(\frac{17}{13}-\frac{4}{13}\right)\times\frac{12}{17}\)                = \((\frac{9}{14}+\frac{5}{14}):\frac{6}{7}\)         = \(\frac{9}{12}\times\frac{9}{7}\times\frac{12}{19}\)

=\(\frac{4}{7}\times1\)                                     = \(1\times\frac{12}{17}\)                                       = \(1:\frac{6}{7}\)                               = \(\frac{9\times9\times12}{12\times7\times19}\)

=\(\frac{4}{7}\)                                              =  \(\frac{12}{17}\)                                                =\(\frac{7}{6}\)                                    = \(\frac{9\times9}{7\times19}=\frac{81}{133}\)

   -  

a,3/5*7/9+11/9*3/5-3/10=3/5*(7/9+11/9)-3/10

=3/5*18/9-3/10

=3/5*2-3/10

=6/5-3/10

=12/10-3/10

=9/10

b,14/13:1/2+3/13*2-2*7/13=14/13*2+3/13*2-2*7/13

=2*(14/13+3/13-7/13)

=2*10/13

=20/13

a/ ( 7/9 + 11/9 ) x 3/5 - 3/10

 =    2 x 3/5 - 3/10

=    6/5  - 3/10

 =    9/10

b/ 14/13 :  1/2 + 3/13 x 2 - 2 x 7/13

14/13 x 2/1 + 3/13 x 2 - 2 x 7/13

2 x ( 14/13 + 3/13 - 7/13 )

2 x 10/13

20/13

1*3+5*7+9*11+...+99*101