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

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

`7/13+5/9+6/13+5/9`

`=(7/13+6/13)+(5/9+5/9)`

`=13/13+10/9`

`=1+10/9`

`=9/9+10/9`

`=19/9`

19/9

Bài 3

a,26/100+0,009+41/100+0,24

0,26+0,09+0,41+0,24

(0,26+0,24)+(0,09+0,41)

0,5+0,5

=1

b,9+1/4+6+2/7+7+3/5+8+2/3+2/5+1/3+5/7+3/4

(9+6+7+8)+(2/7+5/7)+(1/4+3/4)+(3/5+2/5)+(2/3+1/3)

30+1+1+1+1

=34

Bài 4,5 khó quá mik ko bít lamf^^))

Bài 5: vì \(\dfrac{3}{11}\) = \(\dfrac{3\times5}{11\times5}\) = \(\dfrac{15}{55}\)

Vậy Khi giữ nguyên tử số thì số cần thêm vào mẫu số là: 

              55 - 39 = 16

Đáp số: 16 

Bài 4: a, \(\dfrac{2008}{2009}\) < 1; \(\dfrac{10}{9}\) > 1

           \(\dfrac{2008}{2009}\) < \(\dfrac{10}{9}\)

         b, \(\dfrac{1}{a+1}\) và \(\dfrac{1}{a-1}\)

Ta có: a + 1 > a - 1 ⇒ \(\dfrac{1}{a+1}\) < \(\dfrac{1}{a-1}\)

a: =13/26*9/18*2/3=2/3*1/4=2/12=1/6

b: =44/22*5/15*3/2=2*1/3*3/2=2*1/2=1

`5/9xx1/4+4/9xx3/12`

`=5/9xx1/4+4/9xx1/4`

`=1/4xx(5/9+4/9)`

`=1/4xx9/9`

`=1/4xx1`

`=1/4`

5/9.1/4+4/9.1/4=(5/9+4/9).1/4=1.1/4=1/4

\(=\dfrac{3}{7}\left(\dfrac{5}{4}-\dfrac{2}{9}\right)=\dfrac{3}{7}\cdot\dfrac{45-8}{36}=\dfrac{3}{36}\cdot\dfrac{37}{7}=\dfrac{37}{84}\)

\(\dfrac{3}{7}:\dfrac{4}{5}-\dfrac{3}{7}:\dfrac{9}{2}\)
\(=\dfrac{3}{7}\times\dfrac{5}{4}-\dfrac{3}{7}\times\dfrac{2}{9}\)
\(=\dfrac{3}{7}\times\left(\dfrac{5}{4}-\dfrac{2}{9}\right)\)
\(=\dfrac{3}{7}\times\left(\dfrac{45}{36}-\dfrac{8}{36}\right)\)
\(=\dfrac{3}{7}\times\dfrac{37}{36}\)
\(=\dfrac{37}{84}\)
#DatNe

x=3/4-1/8

x=6/8-1/8

x=6/8

=2/5.(9/4-5/4)

=2/5.1

=2/5

\(x=\dfrac{3}{4}-\dfrac{1}{8}\)\(\)

\(x=\dfrac{6}{8}-\dfrac{1}{8}\)

\(x=\dfrac{5}{8}\)

\(=\dfrac{2}{5}x\left(\dfrac{9}{4}-\dfrac{5}{4}\right)\)

\(=\dfrac{2}{5}x1\)

\(=\dfrac{2}{5}\)

`x=3/4-1/8`

`x=5/8`

------------------------

`=2/5xx(9/4+5/4)`

`=2/5xx7/2=5/7`

a, \(=\dfrac{1+4}{5}+\dfrac{5+1+3}{9}=1+1=2\)

b, \(=\dfrac{1+4+2}{3}+\dfrac{1+2+5}{6}=\dfrac{6}{3}+\dfrac{8}{6}=2+\dfrac{4}{3}=\dfrac{6+4}{3}=\dfrac{10}{3}\)

\(\dfrac{17}{20}\) x \(\dfrac{27}{13}\) + \(\dfrac{27}{13}\)  x \(\dfrac{3}{20}\)

= (\(\dfrac{17}{20}\)  + \(\dfrac{3}{20}\)) x \(\dfrac{27}{13}\)

= 1 x \(\dfrac{27}{13}\)

=\(\dfrac{27}{13}\)

Tick cho mik nha