1) Rút gọn các phân số:

$\frac{12}{36}$ = $\frac{1}{3}$

$\frac{49}{84}$ = $\frac{7}{12}$

$\frac{36}{120}$ = $\frac{3}{10}$

$\frac{27}{108}$ = $\frac{1}{4}$

$\frac{75}{145}$ = $\frac{15}{29}$

$\frac{100}{175}$ = $\frac{4}{7}$

2 )

a) Trong các phân số trên , phân số tối giản là : $\frac{49}{51}$ ; $\frac{52}{53}$ ; $\frac{31}{33}$ ; $\frac{41}{43}$ 

b) Rút gọn các phân số còn lại :

$\frac{21}{162}$ = $\frac{7}{54}$

$\frac{435}{560}$ = $\frac{87}{112}$

$\frac{100}{230}$ = $\frac{10}{23}$

3)

$\frac{1}{2}$ + $\frac{1}{3}$ + $\frac{1}{4}$ = $\frac{6}{12}$ + $\frac{4}{12}$ + $\frac{3}{12}$ = $\frac{13}{12}$ 

$\frac{2}{3}$ + $\frac{3}{4}$ + $\frac{4}{5}$ = $\frac{133}{60}$

$\frac{6}{5}$ + $\frac{4}{3}$ + $\frac{9}{7}$ = $\frac{401}{105}$

$\frac{9}{7}$ x $\frac{3}{7}$ = $\frac{27}{49}$

$\frac{8}{9}$ - $\frac{5}{6}$ = $\frac{1}{18}$

$\frac{15}{17}$ - $\frac{11}{13}$ = $\frac{8}{221}$

$\frac{90}{108}$ - $\frac{40 }{72}$ = $\frac{5}{18}$

$\frac{5}{6}$ x $\frac{2}{4}$ = $\frac{5}{12}$

$\frac{9}{12}$ x $\frac{4}{3}$ = 1

4)

X x $\frac{1}{2}$ = $\frac{3}{4}$

 X= $\frac{3}{4}$ : $\frac{1}{2}$

X= $\frac{3}{2}$

$\frac{4}{5}$ x X = 1

  X= 1 : $\frac{4}{5}$

X = $\frac{5}{4}$

X x $\frac{2}{3}$ = $\frac{9}{10}$

X = $\frac{9}{10}$ : $\frac{2}{3}$

X = $\frac{27}{20}$

X : $\frac{2}{3}$ = 150

X = 150 x $\frac{2}{3}$

X = 100

X : $\frac{4}{7}$ = 180

X = 180 x $\frac{7}{4}$

X = $\frac{720}{7}$

$\frac{35}{9}$ : X = $\frac{35}{6}$

X = $\frac{35}{9}$ : $\frac{35}{6}$

X = $\frac{2}{3}$

Đáp án:

1) 12/36=1/3; 36/120=3/10; 49/84=7/12; 27/108=1/4; 75/145=15/29; 100/175=4/7

2) a.phân số tối giản là : 49/51; 52/53; 31/33; 41/43

b.21/162=7/54; 435/560=87/112; 100/230=10/23

3) 1/2+1/3+1/4=13/12

2/3+3/4+4/5=133/60

6/5+4/3+9/7=401/105

9/7*3/7=27/49

8/9*5/6=1/18

15/17-11/13=8/221

90/108-40/72=5/18

5/6*2/4=5/12

9/12*4/3=1

4) x * 1/2=9/10

x=9/10 : 2/3

x= 27/20

4/5*x=1

x=1 : 4/5

x=5/4

x*2/3=9/10

x=9/10 : 2/3

x=27/20

x:2/3=150

x=150*2/3

x=100

x:4/7=180

x=180*4/7

x=120/7

35/9:x=35/6

x=35/6 : 35/9

x=3/2

Giải thích các bước giải: