\(\frac{12}{15}\times\frac{22}{47}+\frac{25}{47}:\frac{15}{12}\)

\(\frac{12}{15}\times\frac{22}{47}+\frac{25}{47}\times\frac{12}{15}\)

\(=\frac{12}{15}\times\left(\frac{22}{47}+\frac{25}{47}\right)\)

\(=\frac{12}{15}\times\frac{22+25}{47}\)

\(=\frac{12}{15}\times1=\frac{12}{15}\)

\(\dfrac{1}{4}\) = 0,25

\(\dfrac{3}{4}\) = 0,75

\(\dfrac{5}{7}\) ≈0,714

\(\dfrac{12}{28}\) ≈ 0,43

\(\dfrac{35}{105}\)≈ 0,33

$1$ = 0,25

$\genfrac{}{}{0ex}{}{3}{4}$ = 0,75

$\genfrac{}{}{0ex}{}{5}{7}$ ≈0,714

$\genfrac{}{}{0ex}{}{12}{28}$ ≈ 0,43

$\genfrac{}{}{0ex}{}{35}{105}$≈ 0,33

a, \(\dfrac{7}{9}\) = \(\dfrac{7\times11}{9\times11}\) = \(\dfrac{77}{99}\)

    \(\dfrac{8}{11}\) = \(\dfrac{8\times9}{11\times9}\) = \(\dfrac{72}{99}\) 

Vậy \(\dfrac{7}{9}\) và \(\dfrac{8}{11}\) đã được quy đồng mẫu số lần lượt thành hai phân số:

      \(\dfrac{77}{99}\) và \(\dfrac{72}{99}\)

b, \(\dfrac{4}{5}\) = \(\dfrac{4\times5}{5\times5}\) = \(\dfrac{20}{25}\)

    Vậy hai phân số \(\dfrac{4}{5}\) và \(\dfrac{7}{25}\) đã được quy đồng mẫu số thành hai phân số: \(\dfrac{20}{25}\) và \(\dfrac{7}{25}\)

Bài 4

35/85 = 7/17

 36/108 = 1/3

 25/100 = 1/4

 39/52 = 3/4

Bài 8

a) 9/8 và 7/12

= 8×3=24 ; 12×2=24

=>9/8 =27/24

=> 7/12 ; 14/24

b) 3/20 và 4/15

=20×3=60 ; 15×4=60

=> 9/60 ; 16/60

Bài 9

a) \(\frac{3}{8},\frac{15}{8},\frac{9}{8},\frac{7}{8}\)

Từ lớn -> bé:

=>\(\frac{15}{8},\frac{9}{8},\frac{7}{8},\frac{3}{8}\)

b) \(\frac{4}{15},\frac{3}{5},\frac{8}{45},\frac{7}{15}=\frac{12}{45},\frac{27}{45},\frac{8}{45},\frac{21}{45}\)

Từ lớn -> bé:

=> \(\frac{3}{5},\frac{7}{15},\frac{4}{15},\frac{8}{45}\)

c) \(\frac{3}{8},\frac{4}{5},\frac{47}{40},\frac{9}{4}=\frac{15}{40},\frac{32}{40},\frac{47}{40},\frac{90}{40}\)

Từ lớn -> bé:

=>\(\frac{9}{4},\frac{47}{40},\frac{4}{5},\frac{3}{8}\)

Bài 10

a, Ta có

`x/15 < 4/15`

` <=> x < 4`

` <=> x ∈ {1 ; 2 ; 3}` 

b, Ta có

`5/9 > x/9`

` <=> 5 > x`

` <=> x ∈ {1 ; 2 ; 3 ; 4}`

c, Ta có

`1 <x/8 < 11/8`

` <=> 8/8 < x/8 < 11/8`

` <=> 8 < x <11`

` <=> x ∈ {9 ; 10}`

a) \(\frac{15}{10}=1,5\)        \(\frac{675}{10}=6,75\)          \(\frac{7}{10}=0,7\)      

\(\frac{79}{100}=0,79\)       \(\frac{5}{100}=0,05\)           \(\frac{67}{100}=0,67\)

b) \(\frac{1}{2}=1\div2=0,5\)                   \(\frac{3}{4}=3\div4=0,75\)

\(\frac{15}{8}=15\div8=1,875\)              \(\frac{7}{25}=7\div25=0,28\)

\(\frac{19}{30}=19\div30=0,63\)              \(\frac{21}{125}=21\div125=0,168\)

\(\frac{15}{3}=5;\frac{25}{4}=6\frac{1}{4};\frac{36}{7}=5\frac{1}{7};\frac{45}{7}=6\frac{3}{7};\frac{25}{3}=8\frac{1}{3};\frac{14}{12}=1\frac{2}{12}=1\frac{1}{6}\)

1.1/2 ; 2/3 ; 3/4 ; 4/5 ; 5/6 .

2. 3/2 ; 13/12 ; 7/8 ; 15/22 .

3. 4/7

4. 5/4

Đáp án là 1/2,2/3,3/4,4/5,5/6,

a)     5/30+15/90+25/150+35/210+45/270

       =1/6+1/6+1/6+1/6+1/6

       =1/6 x 5

       =5/6

b)     1/2+1/6+1/12+1/20+....+1/56

        =1/1x2+1/2x3+1/3x4+1/4x5+.....1/7x8

        =1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+.......-1/7+1/7-1/8

        =1/1-1/8

         =7/8

c)     mình chịu

thank you bn nhìu nha