a: \(=\dfrac{4}{5}+\dfrac{1}{5}\cdot\dfrac{5}{2}=\dfrac{4}{5}+\dfrac{1}{2}=\dfrac{8}{10}+\dfrac{5}{10}=\dfrac{13}{10}\)

b: \(=\dfrac{5}{6}\cdot\dfrac{1}{5}\cdot\dfrac{2}{5}=\dfrac{1}{6}\cdot\dfrac{2}{5}=\dfrac{2}{30}=\dfrac{1}{15}\)

a) \(=\dfrac{13}{10}\)

b) \(=\dfrac{1}{15}\)

a)\(\dfrac{13}{10}\)

b)\(\dfrac{1}{15}\)

Nhìn nó rối ghê á

1: =-15+10-35+28=-32

rối thật đó

1: =-15+10-35+28=-12

3: =20-12-8+12=12

2) -3(4 - 7) + 5(-3 + 2)

= -3.4 + 3.7 - 5.3 + 5.2

= -12 + 21 -15 + 10

= 31 - 27

= 4

4) -5(2 - 7) + 4(2 - 5)

= -5.2 + 5.7 + 4.2 - 4.5

= -10 + 35 + 8 - 20

= 38 - 30

= 8

5) 6(-3 - 7) - 7(3 + 5)

= -6.3 - 6.7 - 7.3 - 7.5

= -18 - 42 - 21 - 35

= -116

6) 3(-5 + 6) - 4(3 - 2)

= -3.5 + 3.6 - 4.3 + 4.2

= -15 + 18 - 12 + 8

= 26 - 27

= -1

3: \(=20-12-8+12=20-8=12\)

5: \(=-18-42-21-35=-116\)

3: \(=-15+18-12+8=-27+26=-1\)

2: \(=-12+21-15+10=9-5=4\)

a: =5/30-12/30=-7/30

b: =-2-5/8=-16/8-5/8=-21/8

c: =6/13-14/39=18/39-14/39=4/39

d: =18/30-25/30=-7/30

e: =-5/9+5/12=-20/36+15/36=-5/36

a) \(\dfrac{-7}{30}\)

b) \(\dfrac{-21}{8}\)

c) \(\dfrac{-7}{30}\)

d) \(\dfrac{-5}{36}\)

\(a,\dfrac{1}{6}+\dfrac{-2}{5}=\dfrac{5}{30}+\dfrac{-12}{30}=\dfrac{-7}{30}\\ b,\left(-2\right)+\dfrac{-5}{8}=\dfrac{-16}{8}+\dfrac{-5}{8}=\dfrac{-21}{8}\\ c,\dfrac{6}{13}+\dfrac{-14}{39}=\dfrac{18}{39}+\dfrac{-14}{39}=\dfrac{4}{39}\\ d,\dfrac{3}{5}-\dfrac{5}{6}=\dfrac{18}{30}-\dfrac{25}{30}=\dfrac{-7}{30}\\ e,\dfrac{-5}{9}-\dfrac{-5}{12}=\dfrac{-20}{36}-\dfrac{-15}{36}=\dfrac{-5}{36}\)

Lời giải:

1.

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

$=3-2+\frac{1}{4}-\frac{1}{3}$

$=1+\frac{1}{4}-\frac{1}{3}=\frac{5}{4}-\frac{1}{3}=\frac{11}{12}$

2. 

$6\frac{5}{9}+2\frac{5}{6}=6+\frac{5}{9}+2+\frac{5}{6}=8+\frac{5}{6}+\frac{5}{9}=8+\frac{25}{18}=8+1+\frac{7}{18}=9+\frac{7}{18}=9\frac{7}{18}$
3.

$6\frac{5}{9}-2\frac{5}{6}=6+\frac{5}{9}-(2+\frac{5}{6})$

$=6+\frac{5}{9}-2-\frac{5}{6}$
$=(6-2)+\frac{5}{9}-\frac{5}{6}$
$=4+\frac{5}{9}-\frac{5}{6}=\frac{41}{9}-\frac{5}{6}=\frac{67}{8}$

\(\dfrac{4}{5}\)+\(\dfrac{-5}{4}\)=\(\dfrac{0}{4}\)

\(\dfrac{-1}{3}\)+\(\dfrac{2}{5}-\dfrac{5}{6}\)=\(\dfrac{-10}{30}+\dfrac{12}{30}-\dfrac{25}{30}\)=\(\dfrac{-23}{30}\)

\(\dfrac{2}{3}-\dfrac{5}{7}.\dfrac{14}{25}\)=\(\dfrac{2}{3}-\dfrac{2}{5}\)=\(\dfrac{10}{15}-\dfrac{6}{15}\)=\(\dfrac{4}{15}\)

a: \(=\dfrac{16-25}{20}=\dfrac{-9}{20}\)

b: \(=\dfrac{-10}{30}+\dfrac{12}{30}-\dfrac{25}{30}=-\dfrac{23}{30}\)

c: \(=\dfrac{2}{3}-\dfrac{1}{5}\cdot2=\dfrac{2}{3}-\dfrac{2}{5}=\dfrac{10-6}{15}=\dfrac{4}{15}\)

d: \(=\dfrac{12-25}{30}\cdot\dfrac{15}{8}-1=\dfrac{-13}{16}-1=\dfrac{-29}{16}\)

e: \(=\dfrac{-3}{13}-\dfrac{10}{13}-\dfrac{7}{17}+\dfrac{24}{17}-\dfrac{5}{19}-\dfrac{14}{19}=-1\)

Lời giải chi tiết:

2,8,10,5,2,8,5,3,4.

5 + 3 + 2 = 10     4 + 4 + 1 = 9     6 + 3 - 5 = 4     5 + 2 - 6 = 1

\(=\dfrac{2}{35}\cdot\dfrac{5}{6}\cdot7+\dfrac{5}{2}\cdot\dfrac{7}{6}\cdot\dfrac{8}{9}\cdot\dfrac{7}{2}=\dfrac{1}{3}+\dfrac{245}{27}=\dfrac{245+9}{27}=\dfrac{254}{27}\)