Ta có: \(\frac{3246}{-3247}=-\frac{3246}{3247}< -1;-\frac{45984}{45983}>-1\)

\(\Rightarrow\frac{3246}{-3247}< -\frac{45984}{45983}\)

Ta có: \(\frac{3246}{-3247}>-1;\frac{-45984}{45983}< -1\)

\(\Rightarrow\frac{3246}{-3247}>\frac{-45984}{45983}\)

Ta so sánh ps đảo ngược của 2 ps sau

\(\frac{68}{23}=2\frac{22}{23};\frac{67}{22}=3\frac{1}{22}Vif2< 3\Rightarrow\frac{68}{23}< \frac{67}{22}\Rightarrow.....\)

Câu b xét 1/2

\(1-\frac{23}{68}=\frac{45}{68}\)

\(1-\frac{22}{67}=\frac{45}{67}\)

Mà \(\frac{45}{68}< \frac{45}{67}\Rightarrow1-\frac{23}{68}< 1-\frac{22}{67}\)

\(\Rightarrow\frac{-23}{68}< \frac{-22}{67}\Rightarrow\frac{23}{68}>\frac{22}{67}\)

ta có 1/3=10/30

1/21+1/22+...+1/30 có 10 p/số

mà 1/21>1/30

1/22>1/30

....

1/29>1/30

1/30=1/30

=>1/21+..1/30>1/30+....1/30 có 10 phân số 

=>1/21+...1/30>1/3

Ta có: \(\frac{1}{21}< \frac{1}{30}\)

\(\frac{1}{22}< \frac{1}{30}\)

......

\(\frac{1}{29}< \frac{1}{30}\)

\(\Rightarrow S< \frac{1}{30}+\frac{1}{30}+...+\frac{1}{30}\)(có 10 p/s)
\(\Rightarrow S< \frac{1}{30}.10=\frac{10}{30}=\frac{1}{3}\)

Vậy S < 1/3

a, Ta có: \(\frac{23}{27}>\frac{23}{29}>\frac{22}{29}\)

\(\Rightarrow\frac{23}{27}>\frac{22}{29}\)

b, Ta có:

\(\frac{12}{25}< \frac{1}{2}\)

\(\frac{25}{49}>\frac{1}{2}\)

\(\Rightarrow\frac{12}{25}< \frac{25}{49}\)

B1:

a,<    b,<

c,<    d,>

e,>    g,>

B2:

a,<    b,<

c,<

b1

a, <

b, <

c, <

d,>

e,>

g, >

a, <

b, <

c,<

a) \(\frac{{21}}{{13}} = \frac{{21.2}}{{13.2}} = \frac{{42}}{{26}}\)

b) \(\frac{{12}}{{ - 25}} = \frac{{12.3}}{{ - 25.3}} = \frac{{36}}{{ - 75}}\)

c) \(\frac{{18}}{{ - 48}} = \frac{{18:6}}{{ - 48:6}} = \frac{3}{{ - 8}}\)

d) \(\frac{{ - 42}}{{ - 24}} = \frac{{ - 42:(-6)}}{{ - 24:( - 6)}} = \frac{7}{4}\).

a: \(\dfrac{21}{13}=\dfrac{21\cdot2}{13\cdot2}=\dfrac{42}{26}\)

b: \(\dfrac{12}{-25}=\dfrac{12\cdot\left(-1\right)}{\left(-25\right)\cdot\left(-1\right)}=\dfrac{-12}{25}\)

c: \(\dfrac{18}{-48}=\dfrac{-18}{48}=\dfrac{-18:6}{48:6}=\dfrac{-3}{8}\)

d: \(\dfrac{-42}{-24}=\dfrac{42}{24}=\dfrac{42:6}{24:6}=\dfrac{7}{4}\)

 a) \(\frac{{ - 3}}{8} = \frac{{ - 3.3}}{{8.3}} = \frac{{ - 9}}{{24}}\)

Vì -9 < -5 nên \(\frac{{ - 9}}{{24}} < \frac{{ - 5}}{{24}}\)

Vậy \(\frac{{ - 3}}{8} < \frac{{ - 5}}{{24}}\).

b) Cách 1: \(\frac{{ - 2}}{{ - 5}} = \frac{2}{5}; \frac{3}{{ - 5}} = \frac{-3}{{5}}\)

Vì 2 > -3 nên \(\frac{2}{5} > \frac{-3}{{5}}\)

Vậy \(\frac{{ - 2}}{{ - 5}} > \frac{3}{{ - 5}}\).

Cách 2: \(\frac{{ - 2}}{{ - 5}} = \frac{2}{5} > 0\) mà \(\frac{3}{{ - 5}} < 0\)

\(\Rightarrow\) \(\frac{{ - 2}}{{ - 5}} > \frac{3}{{ - 5}}\).

c) \(\frac{{ - 3}}{{ - 10}} = \frac{3}{{10}} = \frac{{3.2}}{{10.2}} = \frac{6}{{20}}\)

\(\frac{{ - 7}}{{ - 20}} = \frac{7}{{20}}\)

Vì 6 < 7 nên \(\frac{6}{{20}} < \frac{7}{{20}}\) nên \(\frac{{ - 3}}{{ - 10}} < \frac{{ - 7}}{{ - 20}}\).

d) \(\frac{{ - 5}}{4} = \frac{{ - 5.5}}{{4.5}} = \frac{{ - 25}}{{20}}; \frac{{ 23}}{{-20}}=\frac{{-23}}{{20}} \)

Vì -25 < -23 nên \( \frac{{ - 25}}{{20}} < \frac{{-23}}{{20}} \)

Vậy \(\frac{{ - 5}}{4} < \frac{{23}}{{ - 20}}\).