2 - 5/6 = 2/1 - 5/6 = 12/6 - 5/6 = 12-5/ 6= 7/6

7/8 + 3/4 = 7/8 + 6 / 8 = 7+8/8 = 15/8

2/5 + 3/4 = 8/20 + 15/20 = 8+15/20 = 23/20

2 - 5/6 = 2/1 - 5/6 = 12/6 - 5/6 = 12-5/6 = 7/6

7/8 + 3/4 = 7/8 + 6/8 = 7 + 8/8 =15/8

2/5 + 3/4 = 8/20 + 15/20 = 8 + 15/20 = 23/20

đề??

Chắc là tính ắ;vv

`1/2 -1/3= 3/6 -2/6=1/6`

`1/5 -1/7= 7/35 - 5/35=2/35`

`7/9 -2/5= 35/45 - 18/45=17/45`

`1/2 + 1/3 = 3/6 + 2/6= 5/6`

`2/5 + 1/4 + 1/3 = 24/60 + 15/60 + 20/30=59/30`

`17/42 + 3/7= 17/42 + 18/42=35/42=5/6`

`16/17 - 12/13=4/221`

`a)1/2-1/3`

`=3/6-2/6`

`=1/6`

__

`b)1/5-1/7`

`=7/35-5/35`

`=2/35`

__

`c)7/9-2/5`

`=35/45-18/45`

`=17/45`

__

`d)1/2+1/3`

`=3/6+2/6`

`=5/6`

__

`e)2/5+1/4+1/3`

`=24/60+15/60+20/60`

`=59/60`

__

`g)17/42+3/7`

`=17/42+18/42`

`=35/42`

__

`h|)16/17-12/13`

`=208/221-204/221`

`=4/221`

a: =(5/7+2/7)+(4/3+5/3)=3+1=4

b: =(17/12+7/12)+(29/7-8/7)

=2+3=5

c: =(2/5+3/5)+(6/9+1/3)+(7/4+1/4)

=1+2+1

=4

d: =(1/3+2/3)+(13/17+4/17)+(29/11+4/11)

=1+1+3=5

\(\frac{3}{5}\times\frac{6}{7}+\frac{3}{5}:7+\frac{6}{5}\)

\(=\frac{3}{5}\times\frac{6}{7}+\frac{3}{5}\times\frac{1}{7}+\frac{6}{5}\)

\(=\frac{3}{5}\times\left(\frac{6}{7}+\frac{1}{7}\right)+\frac{6}{5}\)

\(=\frac{3}{5}\times1+\frac{6}{5}\)

\(=\frac{3}{5}+\frac{6}{5}=\frac{9}{5}\)

~ Hok tốt ~

\(\frac{29}{12}:\frac{1}{2}-\frac{5}{12}:\frac{1}{2}-\frac{1}{2}\)

\(=\left(\frac{29}{12}-\frac{5}{12}\right):\frac{1}{2}-\frac{1}{2}\)

\(=2:\frac{1}{2}-\frac{1}{2}\)

\(=4-\frac{1}{2}=\frac{7}{2}\)

~ Hok tốt ~

          Bài 1:

Rút gọn các phân số sau: 

\(\dfrac{12}{24}\) = \(\dfrac{12:12}{24:12}\) = \(\dfrac{1}{2}\)

\(\dfrac{120}{90}\) = \(\dfrac{120:30}{90:30}\) = \(\dfrac{4}{3}\)

\(\dfrac{42}{24}\) = \(\dfrac{42:6}{24:6}\) = \(\dfrac{7}{4}\)

          Bài 2:

Tính bằng cách thuận tiện:

    \(\dfrac{13}{19}\) + \(\dfrac{18}{19}\) + \(\dfrac{17}{19}\) 

=  \(\dfrac{13+18+17}{19}\)

= \(\dfrac{\left(13+17\right)+18}{19}\)

= \(\dfrac{48}{19}\)

\(\dfrac{12}{17}\) + \(\dfrac{19}{17}\) + \(\dfrac{8}{17}\)

= \(\dfrac{12+19+8}{17}\)

= \(\dfrac{\left(12+8\right)+19}{17}\)

= \(\dfrac{39}{17}\)

Bài 1:

\(\frac14+\frac23=\frac{3}{12}+\frac{8}{12}=\frac{3+8}{12}=\frac{11}{12}\)

\(\frac27+\frac23=\frac{6}{21}+\frac{14}{21}=\frac{6+14}{21}=\frac{20}{21}\)

\(\frac25+\frac13=\frac{6}{15}+\frac{5}{15}=\frac{6+5}{15}=\frac{11}{15}\)

\(\frac23+\frac12=\frac46+\frac36=\frac{4+3}{6}=\frac76\)

\(\frac13+\frac35=\frac{5}{15}+\frac{9}{15}=\frac{5+9}{15}=\frac{14}{15}\)
\(\frac45+\frac13=\frac{12}{15}+\frac{5}{15}=\frac{12+5}{15}=\frac{17}{15}\)

\(\frac18+\frac34=\frac18+\frac68=\frac{1+6}{8}=\frac78\)

\(\frac{1}{36}+\frac{5}{12}=\frac{1}{36}+\frac{15}{36}=\frac{1+15}{36}=\frac{16}{36}=\frac49\)

\(\frac13+\frac16+\frac{1}{18}=\frac{6}{18}+\frac{3}{18}+\frac{1}{18}=\frac{6+3+1}{18}=\frac{10}{18}=\frac59\)

Bài 2:

\(\frac{15}{16}-\frac{3}{16}=\frac{15-3}{16}=\frac{12}{16}=\frac34\)

\(\frac{17}{18}-\frac56=\frac{17}{18}-\frac{15}{18}=\frac{17-15}{18}=\frac{2}{18}=\frac19\)

\(\frac34-\frac49=\frac{27}{36}-\frac{16}{36}=\frac{27-16}{36}=\frac{11}{36}\)

\(\frac12-\frac25=\frac{5}{10}-\frac{4}{10}=\frac{5-4}{10}=\frac{1}{10}\)

\(\frac56-\frac{3}{10}=\frac{25}{30}-\frac{9}{30}=\frac{25-9}{30}=\frac{16}{30}=\frac{8}{15}\)

\(3-\frac13=\frac93-\frac13=\frac{9-1}{3}=\frac83\)

\(\frac45-\frac{1}{10}=\frac{8}{10}-\frac{1}{10}=\frac{7}{10}\)

\(\frac52-1=\frac{5-2}{2}=\frac32\)

\(\frac58-\frac25=\frac{25}{40}-\frac{16}{40}=\frac{25-16}{40}=\frac{9}{40}\)

\(1,\\ c,\dfrac{17}{6}-\dfrac{3}{7}-\dfrac{5}{6}=\dfrac{17\times7-3\times6-5\times7}{6\times7}=\dfrac{119-18-35}{42}=\dfrac{66}{42}=\dfrac{11}{7}\\ 2,\\ a,\dfrac{6}{9}+\dfrac{3}{15}+\dfrac{7}{15}\\ =\dfrac{6:3}{9:3}+\dfrac{7+3}{15}\\ =\dfrac{2}{3}+\dfrac{10}{15}\\ =\dfrac{2}{3}+\dfrac{2}{3}\\ =\dfrac{2+2}{3}=\dfrac{4}{3}\)

\(b,\dfrac{7}{2}+\dfrac{29}{12}-\dfrac{11}{12}\\ =\dfrac{7}{2}+\left(\dfrac{29}{12}-\dfrac{11}{12}\right)\\ =\dfrac{7}{2}+\dfrac{29-11}{12}\\ =\dfrac{7}{2}+\dfrac{18}{12}\\ =\dfrac{7}{2}+\dfrac{18:6}{12:6}\\ =\dfrac{7}{2}+\dfrac{3}{2}\\ =\dfrac{7+3}{2}=\dfrac{10}{2}=5\)

\(c,\dfrac{26}{25}-\dfrac{3}{5}-\dfrac{2}{5}\\ =\dfrac{26}{25}-\dfrac{3\times5}{5\times5}-\dfrac{2\times5}{5\times5}\\ =\dfrac{26-15-10}{25}\\ =\dfrac{1}{25}\)

Bài 1:
\(\dfrac{17}{6}-\dfrac{3}{7}-\dfrac{5}{6}=\left(\dfrac{17}{6}-\dfrac{5}{6}\right)-\dfrac{3}{7}=2-\dfrac{3}{7}=\dfrac{14}{7}-\dfrac{3}{7}=\dfrac{11}{7}\)
Bài 2:
a/\(\dfrac{6}{9}+\dfrac{3}{15}+\dfrac{7}{15}\)
\(=\dfrac{2}{3}+\left(\dfrac{3}{15}+\dfrac{7}{15}\right)\)
\(=\dfrac{2}{3}+\dfrac{2}{3}\)
\(=\dfrac{4}{3}\)
b/\(\dfrac{7}{2}+\dfrac{29}{12}-\dfrac{11}{12}\)
\(=\dfrac{7}{2}+\left(\dfrac{29}{12}-\dfrac{11}{12}\right)\)
\(=\dfrac{7}{2}+\dfrac{3}{2}\)
\(=5\)
c/\(\dfrac{26}{25}-\dfrac{3}{5}-\dfrac{2}{5}\)
\(=\dfrac{26}{25}-\left(\dfrac{3}{5}+\dfrac{2}{5}\right)\)
\(=\dfrac{26}{25}-1\)
\(=\dfrac{26}{25}-\dfrac{25}{25}\)
\(=\dfrac{1}{25}\)
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