C

7 × 3 mu x + 20 × 3 mu x = 3 mu 25

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

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) \(\dfrac{2}{9}+\dfrac{5}{9}=\dfrac{7}{9};\dfrac{5}{9}+\dfrac{2}{9}=\dfrac{7}{9}\)

Vậy: \(\dfrac{2}{9}+\dfrac{5}{9}=\dfrac{5}{9}+\dfrac{2}{9}\)

b) \(\dfrac{3}{25}+\dfrac{4}{25}+\dfrac{7}{25}=\dfrac{14}{25};\dfrac{3}{25}+\dfrac{7}{25}+\dfrac{4}{25}=\dfrac{14}{25}\)

Vậy: \(\dfrac{3}{25}+\dfrac{4}{25}+\dfrac{7}{25}=\dfrac{3}{25}+\dfrac{7}{25}+\dfrac{4}{25}\)

1)

2/5x3/4+3/4x3/5

= 3/10+9/20

=6/20+9/20

=3/4

 1)

2/5x3/4+3/4x3/5

= 3/10+9/20

=6/20+9/20

2)

= 41/50-8/25

=41/50-16/50

=1/2

3)

=4/3-10/9

=12/9-10/9

=2/9

=3/4

                                               ngan:3

`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`

-3/8+12/25+5/-8+2/-5+13/25

=(3/8+5/-8)+12/25+2/-5+13/25

=-1+12/25+2/-5+13/25

=-13/25+2/-5+13/25

=-23/25+13/25

=-2/5

hdsghj

Bài 1 :

a) \(...=5^5:5^4=5\)

b) \(...=7^8:7^9=\dfrac{1}{7}\)

c) \(...=2^{15}:\left(2^6.2^5\right)=2^{15}:2^{11}=2^4=16\)

d) \(...=3^{28}:3^{26}=3^2=9\)

Bài 2 :

a) \(...=3^2.3^3:3^4=3^5:3^4=3\)

b) \(...=10^9-10^9=0\)

c) \(...=5^{10}.5^{30}:5^{12}=5^{40}:5^{12}=5^{28}\)

d) \(...=5^{12}:5^9=5^3=125\)

\(\dfrac{6}{25}+\dfrac{3}{5}=\dfrac{6}{25}+\dfrac{15}{25}=\dfrac{21}{25}\)

\(\dfrac{8}{3}-\dfrac{3}{9}=\dfrac{24}{9}-\dfrac{3}{9}=\dfrac{21}{9}=\dfrac{7}{3}\)

\(\dfrac{1}{2}:4=\dfrac{1}{2}\times\dfrac{1}{4}=\dfrac{1}{8}\)

\(\dfrac{3}{2}\times\left(\dfrac{4}{8}+\dfrac{5}{2}\right)=\dfrac{3}{2}\times3=\dfrac{9}{2}\)

\(\dfrac{6}{25}+\dfrac{3}{5}=\dfrac{21}{25}\)

\(\dfrac{8}{3}-\dfrac{3}{9}=\dfrac{7}{3}\)

\(\dfrac{1}{2}\div4=\dfrac{1}{8}\)

\(\dfrac{3}{2}\times\left\{\dfrac{4}{8}+\dfrac{5}{2}\right\}\)

\(=\dfrac{2}{3}\times3\)

\(=2\)