giải:  12/15(2/7+3/7+1/7+1/7)=12/15.7/7=12/15=4/5

\(=\frac{12}{15}.\left(\frac{2}{7}+\frac{3}{7}+\frac{1}{7}+\frac{1}{7}\right)\)

\(=\frac{12}{15}.1\)

\(=\frac{12}{15}=\frac{4}{5}\)

\(7,\)

\(A=7+\left(\dfrac{7}{12}-\dfrac{1}{2}+3\right)-\left(\dfrac{1}{12}+5\right)\)

\(=7+\dfrac{7}{12}-\dfrac{1}{2}+3-\dfrac{1}{12}-5\)

\(=\left(\dfrac{7}{12}-\dfrac{1}{12}\right)+\left(7+3-5\right)-\dfrac{1}{2}\)

\(=\dfrac{6}{12}+5-\dfrac{1}{2}\)

\(=\left(\dfrac{1}{2}-\dfrac{1}{2}\right)+5\)

\(=5\)

\(8,\)

\(A=-\dfrac{1}{4}+\dfrac{7}{33}-\dfrac{5}{3}-\left(-\dfrac{15}{12}+\dfrac{6}{11}-\dfrac{68}{49}\right)\)

\(=-\dfrac{1}{4}+\dfrac{7}{33}-\dfrac{5}{3}+\dfrac{15}{12}-\dfrac{6}{11}+\dfrac{68}{49}\)

\(=\left(-\dfrac{1}{4}+\dfrac{15}{12}\right)+\left(\dfrac{7}{33}-\dfrac{5}{3}-\dfrac{6}{11}\right)+\dfrac{68}{49}\)

\(=\left(-\dfrac{3}{12}+\dfrac{15}{12}\right)+\left(\dfrac{7}{33}-\dfrac{55}{33}-\dfrac{18}{33}\right)+\dfrac{68}{49}\)

\(=\dfrac{12}{12}-\dfrac{66}{33}+\dfrac{68}{49}\)

\(=1-2+\dfrac{68}{49}\)

\(=-1+\dfrac{68}{49}\)

\(=\dfrac{19}{49}\)

\(=\dfrac{11}{12}\left(\dfrac{2}{7}+\dfrac{4}{7}+\dfrac{1}{7}\right)=\dfrac{11}{12}\cdot1=\dfrac{11}{12}\)

=11/12

11/12 nha

a] 4/12 ; 5/12 ; 11/2 ; 1/4

b] 1 ; 9/12; 12/5 ; 11/3

c] 8/21; 6/11;8/7

d] 2/3 ;2/7 15/2

a]1/3  5/12     11/2       1/4

b]1      3/4         12/5         33/9

c]8/21      6/11        8/7

d]2/3        2/7          15/2

a) 1/3 ; 5/12 ; 11/2 ; 1/14

b) 1 ; 9/12 ; 12/5 ; 11/3

c) 8/21 ; 6/11 ; 8/7

d) 2/3 ; 2/7 ; 15/2

7/12 - 2/7 + 1/12 = 7/12 - 1/12 + 2/7 = 1/2 + 2/7 = 11/14

7/12 - 2/7 + 1/12 = 7/12 + 1/12 - 2/7 = 2/3 - 2/7 = 14/21 - 6/21 = 12/21 = 4/7

\(\frac{7}{12}\)\(+\)\(\frac{1}{12}\)\(-\)\(\frac{2}{7}\)\(=\)\(\frac{2}{3}\)\(-\)\(\frac{2}{7}\)\(=\)\(\frac{14}{21}\)\(-\)\(\frac{6}{21}\)\(=\)\(\frac{12}{21}\)\(=\)\(\frac{4}{7}\)

Bài 1

a: 11/12=1-1/12

23/24=1-1/24

mà -1/12>-1/24

nên 11/12>23/24

b: -3/20=-9/60

-7/12=-35/60

mà -9>-35

nên -3/20>-7/12

c) Ta có: \(\dfrac{3}{5}+\dfrac{-5}{20}+\dfrac{30}{75}+\dfrac{-7}{4}\)

\(=\dfrac{3}{5}+\dfrac{2}{5}+\dfrac{-1}{4}+\dfrac{-7}{4}\)

\(=1-2=-1\)

Giải:

a)-1/12+4/3=-1/12+16/12=15/12=5/4

b)(-4/14-3/15)-(1/5-20/35-(-1)).7

=-17/35-22/35.7

=-17/35-22/5

=-171/35

c)3/5+-5/20+30/75+-7/4

=3/5+-1/4+2/5+-7/4

=(3/5+2/5)+(-1/4+-7/4)

=1+-2

=-1

d)5/6.-12/14+7/13

=-5/7+7/13

=-16/91

e)2/-9-5/-36-1/4

=-1/12-1/4

=-1/3

f)2/23+-5/12+7/18+21/23+-7/12

=(2/23+21/23)+(-5/12+-7/12)+7/18

=1+-1+7/18

=7/18

xcsxccsz

\(\frac{15}{32}\)

\(\frac{15}{32}\)