\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{7}+...+\frac{1}{32}-\frac{1}{81}\)

\(=1-\frac{1}{81}\)

\(=\frac{80}{81}\)

Ghi đầy đủ nha

bn có thể ghi rõ ràng đc ko?

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

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

=\(0+\dfrac{5}{13}\) 

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

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

\(=\left(\frac{75}{100}+\frac{1}{4}\right)+\left(\frac{18}{21}+\frac{3}{21}\right)+\left(\frac{19}{32}+\frac{13}{31}\right)\)

\(=1+1+1\)

\(=3\)

Có những phân số chưa tối giản. Tuy nhiên vì đây là bài tính nhanh nên sẽ không rút gọn hết. Xíu quy đồng lại nữa :( Nên chọn lựa ra thôi.

\(\frac{75}{100}=\frac{3}{4}\)

Viết lại có: \(\frac{3}{4}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)

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

          \(=1+1+1\) 

          \(=3\)

= 3 nha banj

75/100+18/21+19/32+1/4+3/21+13/32

=(75/100+1/4)+(18/21+3/21)+(19/32+13/32)

=1+1+1=3

75/100+18/21+19/32+1/4+3/21+13/32

=1/4+75/100+19/32+13/32+3/21+18/21

=1+1+1=3

minh cho ban 1 k nhe 

ồ khó thế ?

Ta có:\(x.\frac{1}{5}+x.\frac{4}{5}=2\)

=>\(x.\frac{1}{5}+\frac{4}{5}=2\)

=>\(x.\frac{5}{5}=2\)

=>\(x.1=2\)

=>\(x=2:1\)

=>\(x=2\)

1. X x 1/5 + X x 4/5 = 2

   X x (1/5 + 4/5)     = 2

   X x 1                  = 2

   X                       = 2 : 1

   X                       = 2

2. 18/21 - 19/32 + 3/21 + 13/32

= (18/21 + 3/21) - (19/32 + 13/32)

= 21/21 - 32/32

= 1 - 1

= 0 

                                                                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

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

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

\(=[8+(\frac{3}{5}+\frac{2}{5})]+[5+(\frac{3}{4}+\frac{1}{4})]\)

\(=(8+1)+(5+1)\)

\(=9+6=15\)

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

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

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

\(=1+1+1=3\)

_Học tốt_

7/100+18/21+19/32+1/4+3/21+13/32

=7/100+(18/21+3/21)+(19/32+13/32)

=7/100+           1        +        1

=            207/100

  7/100+18/21+19/32+1/4+3/21+13/32

=7/100 +      1/4     + (18/21+3/21)+(19/32+13/32)

=7/100+   25/100     +          1         +       1

=8/25                     +                     2

=58/25