12/17:6=2/17

16:8/11=22

9:3/4x4/15=12x4/15=16/5=3,2

A  =\(\frac{2}{5}\times\frac{4}{7}+\frac{3}{5}\times\frac{4}{7}\)  B = \(\frac{17}{13}\times\frac{12}{17}-\frac{4}{13}\times\frac{12}{17}\)   C = \(\frac{9}{14}:\frac{6}{7}+\frac{5}{14}:\frac{6}{7}\)  D =\(\frac{9}{12}:\frac{7}{9}\times\frac{12}{19}\)

=  \(\frac{4}{7}\times\left(\frac{2}{5}+\frac{3}{5}\right)\)              =\(\left(\frac{17}{13}-\frac{4}{13}\right)\times\frac{12}{17}\)                = \((\frac{9}{14}+\frac{5}{14}):\frac{6}{7}\)         = \(\frac{9}{12}\times\frac{9}{7}\times\frac{12}{19}\)

=\(\frac{4}{7}\times1\)                                     = \(1\times\frac{12}{17}\)                                       = \(1:\frac{6}{7}\)                               = \(\frac{9\times9\times12}{12\times7\times19}\)

=\(\frac{4}{7}\)                                              =  \(\frac{12}{17}\)                                                =\(\frac{7}{6}\)                                    = \(\frac{9\times9}{7\times19}=\frac{81}{133}\)

   -  

= (-5/12 + 17/12) + ( 4/37 - 41/37)

= 12/12 + (-37/37)

=1 + (-1)

=0

1 Tính
7/12 - 2/7 + 1/12= (7/12-1/12)+2/7=6/12+2/7=1/2+2/7=7/14+4/14=11/14
12/17-5/17-4/17= 12-5-4/17=3/17

2a, 7/11+3/4+4/11+1/4= (7/11+4/11)+3/4+1/4=11/11+4/4=1+1=2
b)72/99-28/99-14/99= (72-28-14)/99=30/99=10/33

c)69,78+35,97+30,22= (69,78+30,22)+35,97=100+35,97=135,97

d) 83,45-30,98-42,47=83,45-(30,98+42,47)=83,45-73,45=10     

`12/17:4xx1/4`

`=12/17xx1/4xx1/4`

`=12/68xx1/4`

`=(12xx1)/(68xx4)`

`=(3xx1)/(68xx1)`

`=3/68`

\(\dfrac{12}{17}:4\times\dfrac{1}{4}\)
\(=\dfrac{12}{17}\times\dfrac{1}{4}\times\dfrac{1}{4}\)
\(=\dfrac{12}{272}=\dfrac{3}{68}\)

\(\dfrac{12}{17}\)\(:4\) x \(\dfrac{1}{4}\)

= \(\dfrac{12}{17}\) x \(\dfrac{1}{4}\) x \(\dfrac{1}{4}\)

= \(\dfrac{12}{272}\) = \(\dfrac{3}{68}\)

12/17+8/17=20/17+19/17=39/17

a)\(\frac{2}{5}+\frac{3}{4}=\frac{8}{20}+\frac{15}{20}=\frac{23}{20}\)

b)\(\frac{7}{12}-\frac{2}{7}+\frac{1}{12}=\frac{7}{12}+\frac{1}{12}-\frac{2}{7}\)\(=\frac{8}{12}-\frac{2}{7}=\frac{56}{84}-\frac{24}{84}=\frac{32}{84}=\frac{8}{21}\)

c) \(\frac{12}{17}-\frac{5}{17}-\frac{3}{17}=\frac{12-5-3}{17}=\frac{4}{17}\)

Chúc bạn học tốt !

\(123-\left(-77\right)-12.\left(-4\right)+31\)

\(=123+77+48+31\)

\(=279\)