\(=\dfrac{3}{4}.\dfrac{-8}{5}+\dfrac{1}{4}=-\dfrac{6}{5}+\dfrac{1}{4}=-\dfrac{19}{20}\)

\(\left(\dfrac{1}{2020}-\dfrac{2018}{2019}\right):\dfrac{2}{9}-\left(\dfrac{-2019}{2020}+\dfrac{1}{2019}\right):\dfrac{2}{3}=\)

\(\left(\dfrac{1}{2020}-\dfrac{2018}{2019}\right)\cdot\dfrac{3}{2}-\left(\dfrac{-2019}{2020}+\dfrac{1}{2019}\right)\cdot\dfrac{3}{2}=\)

\(\left[\left(\dfrac{1}{2020}-\dfrac{2018}{2019}\right)-\left(\dfrac{-2019}{2020}+\dfrac{1}{2019}\right)\right]\cdot\dfrac{3}{2}=\)

\(\left[\dfrac{1}{2020}-\dfrac{2018}{2019}-\dfrac{2019}{2020}-\dfrac{1}{2019}\right]\cdot\dfrac{3}{2}=\)

\(0\)

\(\dfrac{1}{2}-\dfrac{1}{9}:2+1=\dfrac{13}{9}\)

\(\left(\dfrac{4}{13}-\dfrac{13}{5}\right):\dfrac{4}{5}+\left(\dfrac{9}{13}+\dfrac{3}{5}\right):\dfrac{4}{5}\)

\(=\left(\dfrac{4}{13}-\dfrac{13}{5}\right)\cdot\dfrac{5}{4}+\left(\dfrac{9}{13}+\dfrac{3}{5}\right)\cdot\dfrac{5}{4}\)

\(=\left[\dfrac{4}{13}-\dfrac{13}{5}+\dfrac{9}{13}+\dfrac{3}{5}\right]\cdot\dfrac{5}{4}\)

\(=\dfrac{-5}{4}\)

=(3-5)+(7-9)+.....(319-321)

=(-2)+(-2)+....+(-2)

=(-2) x 160

=(-320)

Ta nhóm 2 số vào một nhóm ta được 160 nhóm có giá trị là -2 ta được -2.160=-320

Nhỏ bấm đúng ch mình nha

ta co

3-5+7-9...-321+319-321

= (3-5)+(7-9)+.....+(319-321)

=-2 + -2 +......+-2

=(-2).160.5

=-321

nhớ ^.^

22. \(\dfrac{\dfrac{3}{4}+\dfrac{3}{7}-\dfrac{3}{8}}{\dfrac{5}{4}+\dfrac{5}{7}-\dfrac{5}{8}}+1=\dfrac{3\left(\dfrac{1}{4}+\dfrac{1}{7}-\dfrac{1}{8}\right)}{5\left(\dfrac{1}{4}+\dfrac{1}{7}-\dfrac{1}{8}\right)}+1=\dfrac{3}{5}+1=\dfrac{8}{5}\)

23. \(\dfrac{2}{5}+\dfrac{3}{5}:\left(\dfrac{3}{5}+\dfrac{-2}{3}\right)+\dfrac{7}{2}=\dfrac{2}{5}+\dfrac{3}{5}:\left(\dfrac{9-10}{15}\right)+\dfrac{7}{2}=\dfrac{2}{5}+\dfrac{3}{5}.\dfrac{-15}{1}+\dfrac{7}{2}=\dfrac{2}{5}-\dfrac{45}{5}+\dfrac{7}{2}\)

\(=\dfrac{4}{10}-\dfrac{90}{10}+\dfrac{35}{10}=\dfrac{4-90+35}{10}=-\dfrac{51}{10}\)

24. \(\dfrac{4+\dfrac{4}{73}-\dfrac{4}{115}}{5+\dfrac{5}{73}-\dfrac{1}{23}}=\dfrac{4\left(1+\dfrac{1}{73}-\dfrac{1}{115}\right)}{5+\dfrac{5}{73}-\dfrac{5}{115}}=\dfrac{4\left(1+\dfrac{1}{73}-\dfrac{1}{115}\right)}{5\left(1+\dfrac{1}{73}-\dfrac{1}{115}\right)}=\dfrac{4}{5}\)

4. \(\dfrac{5}{7}-\dfrac{2}{11}+\dfrac{5}{7}-\dfrac{9}{11}=\dfrac{5}{7}\left(-\dfrac{2}{11}-\dfrac{9}{11}\right)=-\dfrac{5}{7}\)

9. \(\dfrac{5}{9}.\dfrac{7}{13}+\dfrac{5}{9}.\dfrac{9}{13}-\dfrac{5}{9}.\dfrac{3}{13}=\dfrac{5}{9}\left(\dfrac{7}{13}+\dfrac{9}{13}-\dfrac{3}{13}\right)=\dfrac{5}{9}\)

10. \(\dfrac{-5}{9}+\dfrac{8}{15}-\dfrac{2}{11}-\dfrac{4}{9}+\dfrac{7}{15}=\left(-\dfrac{5}{9}-\dfrac{4}{9}\right)+\left(\dfrac{8}{15}+\dfrac{7}{15}\right)-\dfrac{2}{11}=-\dfrac{2}{11}\)

\(\left(1981\times1982-990\right):\left(1980\times1982+992\right)\)

\(=\left(1980\times1982+1982-990\right):\left(1980\times1982+992\right)\)

\(=\left(1980\times1982+992\right):\left(1980\times1982+992\right)\) 

\(=1\)

`-3/7xx15/13-3/7xx11/13-3/7`

`=-3/7xx(15/13+11/13+1)`

`=-3/7xx3`

`=-9/7`

a) 67+135+33

= ( 67+33)+135

= 100 + 135

= 235

b) 146+121+54+379

= ( 146+54)+( 121+379)

= 200 + 500

= 700

c) 198+232-98-32

= ( 232-32)+(198-98)

= 200 + 100

= 300

d)1+2+3+4+.........+50

= ( 50+1) x 50:2 =1275

e)2+4+6+8+..........+100

= ( 100+2) x 50 : 2 =2550

f) 23 x 56 +56

= 1288 + 56

= 1344

g)32 x 19+32

= 608 + 32

= 640

\(a.67+135+33\)

\(=\left(67+33\right)+135\)

\(=100+135=235\)  

\(b.141+121+54+379\)

\(=\left(146+54\right)+\left(121+379\right)\)

\(=200+500=700\)

\(c.198+232-98-32\)

\(=\left(232-32\right)+\left(198-98\right)\)

\(=200+100=300\)

\(f.23.56+56=1288+56=1344\)

\(g.32.19+32=608+32=640\)