/ là chia à

\(\left(1-\frac{3}{10}-x\right):\left(\frac{19}{10}-1-\frac{2}{5}\right)+\frac{4}{5}=1\)

\(\Rightarrow\left(\frac{7}{10}-x\right):\frac{1}{2}+\frac{4}{5}=1\)

\(\Rightarrow\left(\frac{7}{10}-x\right):\frac{1}{2}=\frac{1}{5}\)

\(\Rightarrow\frac{7}{10}-x=\frac{1}{10}\)

\(\Rightarrow x=\frac{3}{5}\)

3 x 15 + 21 x 15 + 85 x 5

= 45 + 315 + 425

= 785

15 - 30 + 40 

= 25

21 + 19 - 50 + 10

= 0

\(\dfrac{1}{5}-\dfrac{1}{4}+2\)

\(=-\dfrac{1}{20}+2\)

\(=\dfrac{39}{20}\)

\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)

\(=\dfrac{5}{12}\times\dfrac{1}{4}\)

\(=\dfrac{5}{12}\times\dfrac{3}{12}\)

\(=\dfrac{5}{48}\)

\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)

\(=-\dfrac{9}{20}\)

\(3\times15+21\times15+85\times5\\ =15\times\left(3+21\right)+425\\ =15\times24+425\\ =360+425\\ =785\)

\(15-30+40\\ =\left(15+40\right)-30\\ =55-30\\ =25\)

\(21+19-50+10\\ =\left(21+19\right)-\left(50-10\right)\\ =40-40\\ =0\)

\(\dfrac{1}{5}-\dfrac{1}{4}+2\)

\(=\dfrac{4}{20}-\dfrac{5}{20}+\dfrac{40}{20}\)

\(=\dfrac{\left(4+40\right)}{20}-\dfrac{5}{20}\)

\(=\dfrac{44}{20}-\dfrac{5}{20}\)

\(=\dfrac{39}{20}\)

\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)

\(=\dfrac{5}{12}\times\dfrac{1}{4}\)

\(=\dfrac{5}{48}\)

\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)

\(=\dfrac{2}{20}+\dfrac{4}{20}-\dfrac{15}{20}\)

\(=\dfrac{6}{20}-\dfrac{15}{20}\)

\(=-\dfrac{9}{20}\)

\(1\dfrac{1}{6}+1\dfrac{1}{4}=\dfrac{7}{6}+\dfrac{5}{4}=\dfrac{14}{12}+\dfrac{15}{12}=\dfrac{14+15}{12}=\dfrac{19}{12}=1\dfrac{7}{12}\)\(2\dfrac{2}{3}\div1\dfrac{3}{19}=\dfrac{8}{3}\div\dfrac{22}{19}=\dfrac{8}{3}\times\dfrac{19}{22}=\dfrac{8\times19}{3\times22}=\dfrac{76}{33}\)

tìm x:

a)x=5/8-1/4
   x=5/8-2/8
   x=3/8
b)x=1/10+3/5
   x=1/10+3/10
   x=4//10
c)  x = 7/8 - 1/4

       x = 5/8

d)x=1/4x3/2
    x=3/8

đ) X = 6/11 : 2/7

     X =6/11x7/2

     X= 21/11

e)X=4/5:2/3

     X=4/5x3/2

     X=12/10=6/5

tính

a) 7/9 x 5/6=35/54

b) 1/5 : 7/10=1/5x10/7

                   =10/35=2/7

c) 6/5 x ( 2/3 - 3/5 )=6/5x(9/15-10/15)

                              =6/5x3/5

                              =18/25

d) 1/4 : 3/8 x 6/5=1/4x8/3x6/5

                           =2/3x6/5

                           =12/15=4/5

không biết có đúng không nhưng đúng nhớ tick cho mình nha,mình cảm ơnn

( 1 - 3/10 - x ) : ( 19/10 - 1 - 2/ 5 ) + 4/5 = 1 

=> (7/10 - x) : (9/10 - 2/5) = 1 - 4/5

=> (7/10 - x) : 1/2              = 3/5

=> (7/10 - x)                      = 3/5 : 1/2 

=> 7/10 - x                         = 6/5

=> x                                   = 7/10 - 6/5

=> x                                   = -1/2

ko ghi lại đề

=>(7/10-x):1/2+4/5=1

=>(7/10-x):1/2=1/5

=>7/10-x=1/10

=>x=3/5

19 x 1 = 19

19 x 2 = 38

19 x 3 = 57

19 x 4 = 76

19 x 5 = 95

19 x 6 = 114

19 x 7 = 133

19 x 8 = 152

19 x 9 = 172

19 x 10 = 190

Hok tốt ah

19

38

57

76

95

114

133

152

171

190

\(a.\frac{19}{5}\cdot\frac{4}{7}+\frac{3}{7}\cdot\frac{19}{5}-\frac{4}{5}\)

\(=\frac{19}{5}\cdot\left(\frac{4}{7}+\frac{3}{7}\right)-\frac{4}{5}\)

\(=\frac{19}{5}\cdot1-\frac{4}{5}\)

\(=\frac{19}{5}-\frac{4}{5}=\frac{15}{5}=3\)

\(b.2\frac{2}{7}\cdot5\frac{2}{5}+\frac{16}{7}\cdot1\frac{3}{5}+\frac{1}{2}\)

\(=\frac{16}{7}\cdot\frac{27}{5}+\frac{16}{7}\cdot\frac{8}{5}+\frac{1}{2}\)

\(=\frac{16}{7}\cdot\left(\frac{27}{5}+\frac{8}{5}\right)+\frac{1}{2}\)

\(=\frac{16}{7}\cdot7+\frac{1}{2}\)

\(=16+\frac{1}{2}=\frac{33}{2}\)

\(c.\frac{3}{7}\cdot3\frac{3}{4}-\frac{3}{7}\cdot\frac{5}{4}-\frac{1}{4}\)

\(=\frac{3}{7}\cdot\frac{15}{4}-\frac{3}{7}\cdot\frac{5}{4}-\frac{1}{4}\)

\(=\frac{3}{7}\cdot\left(\frac{15}{4}-\frac{5}{4}\right)-\frac{1}{4}\)

\(=\frac{3}{7}\cdot\frac{5}{2}-\frac{1}{4}\)

\(=\frac{15}{14}-\frac{1}{4}=\frac{23}{28}\)

Chú ý: \(\cdot:\times\)

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10=55

2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20=110

1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19=100

k mk nha pạn hiền!

10 +1 = 11 có 10 số vậy thì 10 : 2 = 5 thì sẽ bằng 5x11 = 55

2 + 20 = 22 cũng có 10 số lấy 10 : 2 = 5 se bang 22 x5 = 110

1+19 = 20 , 10 : 2 = 5 , 20x5 = 100

a ) 10 x X - 1 - 3 - 5 - 7 - ... - 19 = 2 + 4 + 6 + ... + 20

10 x X - 1 - 3 - 5 - 7 - ... - 19 = 110

10 x X - ( 1 + 3 + 5 + 7 + ... + 19 ) = 110

10 x X - 100 = 110

10 x X = 110 + 100

10 x X = 210

       X = 210 : 10

       X = 21

a 10 x X-1-3-5-7-....-19 = 2+4+6+....+20

​10xX-1-3-5-7-....-19=110

​10xX=110+1+3+5+7+....+19

​10xX=210

​X=210:10

​X=21

b là 4

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a)\(3:\left(2x+1\right)=72-69\)

\(3:\left(2x+1\right)=3\)

\(2x+1=3:3\)

\(2x+1=1\)

\(2x=1-1\)

\(2x=0\)

\(x=0:2\)

\(x=0\)

các bài còn lại giống như câu a nha nếu ko biết thì comment lại minhf sẽ giải cho . Nhớ k cho mình nha