a) Cách 1 : (3/4 + 1/2) x 5/7

               = 5/4 x 5/7

                = 25/28

Cách 2 : (3/4 + 1/2) x 5/7

           = 3/4 x 5/7 + 1/2 x 5/7

            = 15/28 + 5/14

            = 25/28

b) Cách 1 : 5/7 x 13/21 + 2/7 x 13/21

= 65/147 + 26/147

= 13/21

Cách 2 : 5/7 x 13/21 + 2/7 x 13/21

= (5/7 + 2/7) x 13/21

= 1 x 13/21

= 13/21

câu c tự làm

8 /15 :2/3+7/15:2/3 =                                              tính bằng 2 cách nhé các bạn

Cách 1:6/8+4/8+5/7=10/8*5/7=50/56=25/28

Cách 2 :3/4*5/7+1/2*
5/7=15/28+10/28=25/28

Cái này thầy tôi đã chữa yên tâm

a)  \(\frac{3}{4}\times\frac{1}{2}\times2\)

C1: \(=\frac{3}{8}\times2=\frac{3}{4}\)

C2:  \(=\frac{3}{4}\times1=\frac{3}{4}\)

b)  \(\left[\frac{3}{4}+\frac{1}{2}\right]\times\frac{5}{7}\)

C1:  \(=\frac{5}{4}\times\frac{5}{7}=\frac{25}{28}\)

C2:   \(=\frac{3}{4}\times\frac{5}{7}+\frac{1}{2}\times\frac{5}{7}=\frac{15}{28}+\frac{5}{14}=\frac{25}{28}\)

a/\(\frac{3}{4}\cdot\frac{1}{2}\cdot2=\frac{6}{8}\cdot2=\frac{12}{8}=\frac{3}{2}\)

\(\frac{3}{4}\cdot\frac{1}{2}\cdot2=\frac{3}{4}\cdot\frac{2}{2}=\frac{3}{4}\cdot1=\frac{3}{4}\)

b/\(\left(\frac{3}{4}+\frac{1}{2}\right)\cdot\frac{5}{7}=\frac{5}{4}\cdot\frac{5}{7}=\frac{25}{28}\)

\(\left(\frac{3}{4}+\frac{1}{2}\right)\cdot\frac{5}{7}=\frac{3}{4}\cdot\frac{5}{7}+\frac{1}{2}\cdot\frac{5}{7}=\frac{15}{28}+\frac{5}{14}=\frac{15}{28}+\frac{10}{28}=\frac{25}{28}\)

c/\(\frac{5}{7}\cdot\frac{13}{21}+\frac{2}{7}\cdot\frac{13}{21}=\frac{65}{147}+\frac{26}{147}=\frac{91}{147}=\frac{13}{21}\)

\(\frac{5}{7}\cdot\frac{13}{21}+\frac{2}{7}\cdot\frac{13}{21}=\left(\frac{5}{7}+\frac{2}{7}\right)\cdot\frac{13}{21}=1\cdot\frac{13}{21}=\frac{13}{21}\)

Học tốt @#_#@

<br class="Apple-interchange-newline"><div id="inner-editor"></div>34 ·12 ·2=68 ·2=128 =32 

34 ·12 ·2=34 ·22 =34 ·1=34 

b/(34 +12 )·57 =54 ·57 =2528 

(34 +12 )·57 =34 ·57 +12 ·57 =1528 +514 =1528 +1028 =2528 

c/57 ·1321 +27 ·1321 =65147 +26147 =91147 =1321 

57 ·1321 +27 ·1321 =(57 +27 )·1321 =1·1321 =1321 

Học tốt @#_#@

 Đúng 0  Sai 0

Phạm Trà My

<br class="Apple-interchange-newline"><div id="inner-editor"></div>34 ·12 ·2=68 ·2=128 =32 

34 ·12 ·2=34 ·22 =34 ·1=34 

b/(34 +12 )·57 =54 ·57 =2528 

(34 +12 )·57 =34 ·57 +12 ·57 =1528 +514 =1528 +1028 =2528 

c/57 ·1321 +27 ·1321 =65147 +26147 =91147 =1321 

57 ·1321 +27 ·1321 =(57 +27 )·1321 =1·1321 =1321 

Trình bày hết ra thì dài lắm. Mình nói cái chính rồi bạn làm nốt.

Cách 1 ở tất cả các câu: Tính bình thường như đề cho

 a)   Cách 2: \(\frac{5}{7}\times\frac{3}{4}+\frac{5}{7}\times\frac{1}{2}\)

 b) Cách 2: \(\frac{13}{21}\times\left(\frac{5}{7}+\frac{2}{7}\right)\)

c) Cách 2: \(\frac{2}{5}\times\frac{1}{2}+\frac{2}{5}\times\frac{1}{3}\)

d) Cách 2: \(\frac{17}{21}\times\left(5+\frac{2}{5}\right)\)

a) Cách 1

\(\frac{3}{4}\)x \(\frac{1}{2}\)x \(2\)

= \(\frac{3}{8}\)x \(2\)

= \(\frac{3}{4}\)

Cách 2

\(\frac{3}{4}\)x \(\frac{1}{2}\)x \(2\)

= \(\frac{3}{4}\)x \(\left(\frac{1}{2}x2\right)\)

= \(\frac{3}{4}\)x 1

= \(\frac{3}{4}\)

                                                                Bài giải

a, \(\frac{4}{5}-\frac{2}{3}+\frac{1}{5}-\frac{1}{3}\)

\(=\left(\frac{4}{5}+\frac{1}{5}\right)-\left(\frac{2}{3}+\frac{1}{3}\right)=1-1=0\)

b, \(\frac{2}{5}\text{ x }\frac{7}{4}-\frac{2}{5}\text{ x }\frac{3}{7}\)

\(=\frac{2}{5}\text{ x }\left(\frac{7}{4}-\frac{3}{7}\right)=\frac{2}{5}\text{ x }\frac{37}{28}=\frac{37}{70}\)

c, \(\frac{13}{4}\text{ x }\frac{2}{3}\text{ x }\frac{4}{13}\text{ x }\frac{3}{12}=\frac{13\text{ x }2\text{ x }4\text{ x }3}{4\text{ x }3\text{ x }13\text{ x }12}=\frac{1}{6}\)

d,  \(\frac{75}{100}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)

\(=\frac{3}{4}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)

\(=\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{18}{21}+\frac{3}{21}\right)+\left(\frac{19}{32}+\frac{13}{32}\right)\)

\(=1+1+1\)

\(=3\)

e, \(\frac{2}{5}+\frac{6}{9}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)

\(=\frac{2}{5}+\frac{2}{3}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)

\(=\frac{1}{5}\left(2+3\right)+\frac{1}{3}\left(2+1\right)+\frac{1}{4}\left(3+1\right)\)

\(=\frac{1}{5}\cdot5+\frac{1}{3}\cdot3+\frac{1}{4}\cdot4\)

\(=1+1+1\)

\(=3\)

a, \(\frac{4}{5}-\frac{2}{3}+\frac{1}{5}-\frac{1}{3}\)

\(=\left(\frac{4}{5}+\frac{1}{5}\right)-\left(\frac{2}{3}+\frac{1}{3}\right)=1-1=0\)

b, \(\frac{2}{5}\text{ x }\frac{7}{4}-\frac{2}{5}\text{ x }\frac{3}{7}\)

\(=\frac{2}{5}\text{ x }\left(\frac{7}{4}-\frac{3}{7}\right)=\frac{2}{5}\text{ x }\frac{37}{28}=\frac{37}{70}\)

c, \(\frac{13}{4}\text{ x }\frac{2}{3}\text{ x }\frac{4}{13}\text{ x }\frac{3}{12}=\frac{13\text{ x }2\text{ x }4\text{ x }3}{4\text{ x }3\text{ x }13\text{ x }12}=\frac{1}{6}\)

d,  \(\frac{75}{100}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)

\(=\frac{3}{4}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)

\(=\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{18}{21}+\frac{3}{21}\right)+\left(\frac{19}{32}+\frac{13}{32}\right)\)

\(=1+1+1\)

\(=3\)

e, \(\frac{2}{5}+\frac{6}{9}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)

\(=\frac{2}{5}+\frac{2}{3}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)

\(=\frac{1}{5}\left(2+3\right)+\frac{1}{3}\left(2+1\right)+\frac{1}{4}\left(3+1\right)\)

\(=\frac{1}{5}\cdot5+\frac{1}{3}\cdot3+\frac{1}{4}\cdot4\)

\(=1+1+1\)

\(=3\)

a ,            =(4/5+1/5)-(2/3+1/3)=1-1=0

  b   ,            =2/5 x (7/4-3/7) =2/5 x 37/28 =74/140=37/70

c,             =13/4 x 2/3 x 13/4  x 2/3=26/12 x 26/12= 13/6 x 13/6 =13 x 13/6 x 6(gạch 13 trên tử thì tử còn 1 x 13,mẫu hết.) =1 x 13/1=13

d,               =3/4+6/7+19/32 +1/4+1/7 +13/32=(3/4+1/4 )+(6/7+1/7)+(19/32+13/32)=1+1+1=3

e,            =(2/5+3/5)+(2/3+1/3)+(3/4+1/4) [6/9 rút gọn thành 2/3] =1+1+1=3

Ghi đầy đủ nha

bn có thể ghi rõ ràng đc ko?

a)\(-\dfrac{3}{7}+\dfrac{5}{13}+\dfrac{3}{7}\) 

=\(\left(-\dfrac{3}{7}+\dfrac{3}{7}\right)+\dfrac{5}{13}\) 

=\(0+\dfrac{5}{13}\) 

=\(\dfrac{5}{13}\)

Nhào vô trả lời nhanh và đúng mk k cho!!!

nhanh! nhanh ! nhanh

có dấu ngoặc đơn ko