\(1,\dfrac{12}{25}+\dfrac{3}{5}+\dfrac{13}{25}=\left(\dfrac{12}{25}+\dfrac{13}{25}\right)+\dfrac{3}{5}=1+\dfrac{3}{5}=\dfrac{8}{5}\\ 2,\dfrac{3}{2}+\dfrac{2}{3}+\dfrac{4}{3}=\dfrac{3}{2}+\left(\dfrac{2}{3}+\dfrac{4}{3}\right)=\dfrac{3}{2}+2=\dfrac{7}{2}\\ 3,\dfrac{3}{2}+\dfrac{7}{5}+\dfrac{3}{4}=\left(\dfrac{3}{2}+\dfrac{3}{4}\right)+\dfrac{7}{5}=\left(\dfrac{6}{4}+\dfrac{3}{4}\right)+\dfrac{7}{5}=\dfrac{9}{4}+\dfrac{7}{5}=\dfrac{45}{20}+\dfrac{28}{20}=\dfrac{73}{20}\)

Quy đồng 3/5 cho cùng mẫu chung là 25 có

12/25+15/25+13/25=40/25=8/5

Mẫu chung là 6 có

9/6+4/6+8/6=21/6=7/2

Quy đồng mẫu chung là 20 có

30/20+28/30+15/20=73/20

Chúc em học tốt

     12/25 + 3/5 + 13/25 = (12/25 +13/25) + 3/5 = 1 + 3/5 = 8/5

   3/2 + 2/3 + 4/3 =3/2  + ( 2/3+4/3 ) = 7/2

    3/2 + 7/5 + 3/4 = ( 3/2+3/4) + 7/5 = 12/5

\(a,\frac{12}{25}+\frac{3}{5}+\frac{13}{25}\)

\(=\left(\frac{12}{25}+\frac{13}{25}\right)+\frac{3}{5}\)

\(=\frac{25}{25}+\frac{3}{5}\)

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

\(=\frac{8}{5}\)

\(b,\frac{3}{2}+\frac{2}{3}+\frac{4}{3}\)

\(=\frac{3}{2}+\left(\frac{2}{3}+\frac{4}{3}\right)\)

\(=\frac{3}{2}+2\)

\(=\frac{7}{2}\)

\(c,\frac{3}{5}+\frac{7}{5}+\frac{3}{4}\)

\(=\left(\frac{3}{5}+\frac{7}{5}\right)+\frac{3}{4}\)

\(=2+\frac{3}{4}\)

\(=\frac{11}{4}\)

`a: =(7/3-4/3)+11/5=16/5`

`b: =(18/13-5/13)+55/46=1+55/46=101/46`

`c: =27/25-4/9-2/25+5/9=(27/25-2/25)+(5/9-4/9)=1+1/9=10/9`

a) \(\frac{12}{25}+\frac{3}{5}+\frac{134}{25}=\left(\frac{12}{25}+\frac{134}{25}\right)+\frac{3}{5}=\frac{146}{25}+\frac{3}{5}=\frac{146}{25}+\frac{15}{25}=\frac{161}{25}\)

b) \(\frac{3}{2}+\frac{2}{3}+\frac{4}{3}=\frac{3}{2}+\left(\frac{2}{3}+\frac{4}{3}\right)=\frac{3}{2}+\frac{6}{3}=\frac{9}{6}+\frac{12}{6}=\frac{21}{6}=\frac{7}{2}\)

c) \(\frac{3}{5}+\frac{7}{5}+\frac{3}{4}=\left(\frac{3}{5}+\frac{7}{5}\right)+\frac{3}{4}=\frac{10}{5}+\frac{3}{4}=2+\frac{3}{4}=\frac{8}{4}+\frac{3}{4}=\frac{11}{4}\)

a,\(\frac{12}{25}+\frac{3}{5}+\frac{134}{25}=\frac{12}{25}+\frac{15}{25}+\frac{134}{25}=\frac{161}{25}\)

b, \(\frac{3}{2}+\frac{2}{3}+\frac{4}{3}=\frac{3}{2}+\left(\frac{2}{3}+\frac{4}{3}\right)=\frac{3}{2}+\frac{6}{3}=\frac{3}{2}+2=\frac{7}{2}\)

c, \(\left(\frac{3}{5}+\frac{7}{5}\right)+\frac{3}{4}=\frac{10}{5}+\frac{3}{4}=2+\frac{3}{4}=\frac{11}{4}\)

8/15+2/3=18/15=6/5                                                                                                                                        3/8+4/8=7/8                                                                                                                                                  tính thuận tiện:                                                                                                                                              3/2+2/3+4/3=3/2+(2/3+4/3)=3/2+2=7/2                                                                                                             3/5+7/5+3/4=(3/5+7/5)+3/4=2+3/4=11/4                                                                                                           hình như cái đầu tiên chép sai đề????????????????                     

ai bảo trong sách viết vậy mà

8/15+2/3=8/15+10/15=18/15=6/5

3/8+4/8=7/8.  Nha bạn chúc bạn hok tốt

a) (12/25 + 13/25) + 3/5

= 25/25 + 3/5 

= 25/25 + 15/25

= 40/25 = 8/5

b) 3/2 + ( 2/3 + 4/3)

=  3/2 + 1/3

=  15/6

c) ( 3/5 + 7/5) + 3/4

=  10/5 + 3/4

= 55/20 = 11/4

hok tot

nho k nhe

giải : ( ko chép lại đề ....... tự chép )

a) \(\frac{3}{5}\)+(  \(\frac{12}{25}\) + \(\frac{13}{25}\))

= \(\frac{3}{5}\)+           1

= \(\frac{8}{5}\)

b) \(\frac{3}{2}\)+   ( \(\frac{2}{3}\)+\(\frac{4}{3}\))

=   \(\frac{3}{2}\)+       2

=   \(\frac{7}{2}\)

c) (\(\frac{3}{5}\)+ \(\frac{7}{5}\))+ \(\frac{3}{4}\)

=      2                   + \(\frac{3}{4}\)

= \(\frac{11}{4}\)

hok tốt nha !!!