1.1) 6

 1.2) 1/6
 

\(3\div\frac{1}{2}=3\times\frac{2}{1}=6\)

\(\frac{1}{2}\div3=\frac{1}{2}\times\frac{1}{3}=\frac{1}{6}\)

2.Tính theo mẫu :

b) \(\frac{6}{25}\div\frac{21}{20}=\frac{6}{25}\times\frac{20}{21}=\frac{6\times20}{25\times21}=\frac{2\times3\times4\times5}{5\times5\times3\times7}=\frac{8}{35}\)

\(\frac{40}{7}\times\frac{14}{5}=\frac{40\times14}{7\times5}=\frac{5\times8\times7\times2}{7\times5}=16\)

\(\frac{17}{13}\div\frac{51}{26}=\frac{17}{13}\times\frac{26}{51}=\frac{17\times13\times2}{13\times17\times3}=\frac{2}{3}\)

Chúc bạn hok tốt !

a) Viết thương của mỗi phép chia sau dưới dạng phân số (theo mẫu).

13 : 17 = \(\dfrac{13}{17}\)

 21 : 11 = \(\dfrac{22}{11}\)      

40 : 51 = \(\dfrac{40}{51}\)       

72 : 25 = \(\dfrac{72}{25}\)

b) Viết (theo mẫu)

34 : 17 = \(\dfrac{34}{17}\) = 2

20 : 5 =\(\dfrac{20}{5}\) = 4

42 : 42 = \(\dfrac{42}{42}\) = 1         

0 : 6 = \(\dfrac{0}{6}\) = 0

b)\(4\times\dfrac{3}{8}=\dfrac{12}{8}=\dfrac{3}{2}\)

    \(3:\dfrac{1}{2}\) 

   =\(3\times\dfrac{2}{1}\)

  =  6   

  =\(\dfrac{1}{2}:3\)

  = \(\dfrac{1}{2}\times\dfrac{1}{3}\)

  = \(\dfrac{1}{6}\)

1a, \(\dfrac{3}{10}\) \(\times\) \(\dfrac{4}{9}\) 

= \(\dfrac{3\times2\times2}{2\times5\times3\times3}\) 

= \(\dfrac{2}{15}\)

\(\dfrac{6}{5}\): \(\dfrac{3}{7}\)

= \(\dfrac{6}{5}\) \(\times\) \(\dfrac{7}{3}\)

= \(\dfrac{14}{5}\)

\(\dfrac{3}{4}\) \(\times\) \(\dfrac{2}{5}\)

= \(\dfrac{3\times2}{2\times2\times5}\)

= \(\dfrac{3}{10}\)

\(\dfrac{5}{8}\) : \(\dfrac{1}{2}\)

= \(\dfrac{5}{8}\) \(\times\) \(\dfrac{2}{1}\)

= \(\dfrac{5}{4}\)

500/1000:10=50/100

18/200:2=9/100

6/25x4=24/100

6/25= 24/100 (nhân cho 4)

500/1000 = 50/100( chia cho 10)

18/200= 9/100  (chia cho 2)

Bài 2 : 

a, \(3+\dfrac{2}{5}\)

= \(\dfrac{15}{5}+\dfrac{2}{5}\)

= \(\dfrac{17}{5}\)

b, \(4-\dfrac{5}{7}\)

= \(\dfrac{28}{7}-\dfrac{5}{7}\)

= \(\dfrac{23}{7}\)

c, \(1-\left[\dfrac{2}{5}+\dfrac{1}{3}\right]\)

= \(1-\left[\dfrac{6}{15}+\dfrac{5}{15}\right]\)

= \(\dfrac{15}{15}-\dfrac{11}{15}\)

= \(\dfrac{4}{15}\)

Bài 2

a, 3 + \(\dfrac{2}{5}\) = \(\dfrac{15}{5}\) + \(\dfrac{2}{5}\) = \(\dfrac{17}{5}\)

 b, 4 - \(\dfrac{5}{7}\) = \(\dfrac{28}{7}\) - \(\dfrac{5}{7}\) = \(\dfrac{23}{7}\)

c, 1 - ( \(\dfrac{2}{5}\) + \(\dfrac{1}{3}\))

= 1 - (\(\dfrac{6}{15}\) + \(\dfrac{5}{15}\))

= 1 - \(\dfrac{11}{15}\)

= \(\dfrac{15}{15}\) - \(\dfrac{11}{15}\)

= \(\dfrac{4}{15}\)

BAI 1 ; 

Bài 2: 

a, \(\dfrac{5}{23}\) \(\times\) \(\dfrac{17}{26}\) + \(\dfrac{5}{23}\) \(\times\) \(\dfrac{9}{26}\) 

= \(\dfrac{5}{23}\) \(\times\) ( \(\dfrac{17}{26}\) + \(\dfrac{9}{26}\))

= \(\dfrac{5}{23}\) \(\times\) \(\dfrac{26}{26}\)

= \(\dfrac{5}{23}\) 

b, \(\dfrac{3}{4}\) \(\times\) \(\dfrac{7}{9}\) + \(\dfrac{7}{4}\)  \(\times\) \(\dfrac{3}{9}\)

= \(\dfrac{7}{12}\) + \(\dfrac{7}{12}\)

= \(\dfrac{14}{12}\)

= \(\dfrac{7}{6}\)

a)-13-10-8-12

=-(13+10+8+12)=>-43

b)-14-7-12-21

=-(14+7+12+21)=>-54

c)-5-9-11-24

=-(5+9+11+24)=>-49

d)-6-8-13-17

=-(6+8+13+17)=>-44

e)-10-14-16-15

=-(10+14+16+15)=>-55

g)-3-7-25-45

=-(3+7+25+45)=>-80

tick cho mk nha bạn

a) = - (13 + 10 + 8 + 12) = - 43 

14/₇₀ = 0,2

11/₂₅ = 0,44

75/₃₀₀ = 0,25

23/₅₀₀ = 0,046

400+400=800

b, \(\dfrac{3}{5}\) - \(\dfrac{3}{8}\)

= \(\dfrac{24}{40}\) - \(\dfrac{15}{40}\)

= \(\dfrac{9}{40}\)

c, \(\dfrac{1}{4}\) + \(\dfrac{5}{6}\) 

= \(\dfrac{6}{24}\) + \(\dfrac{20}{24}\) 

= \(\dfrac{26}{24}\) 

= \(\dfrac{13}{12}\)