Lời giải:

a.

$(-6)+|83|-(-75)+|-37|=-6+83+75+37=-6+195=195-6=189$

b.

$(-12)-(-26)-[(-9)-|21|)=-12+26-(-9-21)=-12+26+(9+21)$

$=-12+26+30=-12+56=56-12=44$

c.

$15-(-48)-15+(-17)-|-48|=15+48-15-17-48$

$=(15-15)+(48-48)-17=-17$

d.

$-24-(-33)+|24|-(-|78|)-|33|-78$

$=-24+33+24+78-33-78$

$=(-24+24)+(33-33)+(78-78)=0$

thanks bro

\(A=\dfrac{7}{19}\times\dfrac{8}{11}+\dfrac{7}{19}\times\dfrac{3}{11}+\dfrac{12}{19}\)

\(=\dfrac{7}{19}\left(\dfrac{8}{11}+\dfrac{3}{11}\right)+\dfrac{12}{19}\)

\(=\dfrac{7}{19}+\dfrac{12}{19}=\dfrac{19}{19}=1\)

a: \(A=\dfrac{7}{19}\left(\dfrac{8}{11}+\dfrac{3}{11}\right)+\dfrac{12}{19}=\dfrac{7}{19}+\dfrac{12}{19}=1\)

b: \(B=\left(\dfrac{67}{111}+\dfrac{2}{33}-\dfrac{5}{117}\right)\cdot\dfrac{4-3-1}{12}=0\)

a: \(=\dfrac{31}{23}-\dfrac{7}{32}-\dfrac{8}{23}=1-\dfrac{7}{32}=\dfrac{25}{32}\)

b: \(=\dfrac{38}{45}-\dfrac{8}{45}+\dfrac{1}{3}+\dfrac{3}{11}=\dfrac{30}{45}+\dfrac{1}{3}+\dfrac{3}{11}=1+\dfrac{3}{11}=\dfrac{14}{11}\)

c: \(=\dfrac{1}{3}+\dfrac{12}{67}+\dfrac{13}{41}-\dfrac{79}{67}+\dfrac{28}{41}\)

\(=\dfrac{1}{3}-1+1=\dfrac{1}{3}\)

Bài 1: 

Trong 1 giờ, người thứ nhất làm được 1/4(công việc)

Trong 1 giờ, người thứ hai làm được 1/7(công việc)

Nếu làm chung thì mỗi giờ hai người làm được:

1/4+1/7=11/28(công việc)

cx đc đó mà :(

Câu 5: 

a: \(\Leftrightarrow2x=50\)

hay x=25

6A:

a: \(A=-5-7-8=-20\)

b: \(=-2+5+8=11\)

c: \(=20-7+8:4=13+2=15\)

d: \(=-7\cdot\left(-10\right)+\left(-10\right):\left(-5\right)-20=70-20+2=52\)

7A:

a: \(=83+234-34+17=100+200=300\)

d: =17(15+85)-120

=1700-120

=1580

b: \(=645+64-645+36=100\)

e: =79(-79-21)

=79*(-100)

=-7900

z4:

\(\dfrac{24}{148}=\dfrac{6}{37}=\dfrac{108}{37\cdot18}\)

\(\dfrac{-14}{-36}=\dfrac{7}{18}=\dfrac{7\cdot37}{18\cdot37}=\dfrac{259}{37\cdot18}\)

mà 108<259

nên \(\dfrac{24}{148}< \dfrac{-14}{-36}\)

z5: \(\dfrac{-26}{-72}=\dfrac{26}{72}< 1\)

\(1< \dfrac{45}{20}=\dfrac{-45}{-20}\)

Do đó: \(\dfrac{-26}{-72}< \dfrac{-45}{-20}\)

z6: \(\dfrac{14}{42}=\dfrac{1}{3}=\dfrac{1\cdot4}{3\cdot4}=\dfrac{4}{12}\)

\(\dfrac{21}{28}=\dfrac{3}{4}=\dfrac{3\cdot3}{4\cdot3}=\dfrac{9}{12}\)

mà 4<9

nên \(\dfrac{14}{42}< \dfrac{21}{28}\)

z7: \(\dfrac{-14}{-56}=\dfrac{1}{4}=\dfrac{5}{20}\)

\(\dfrac{21}{35}=\dfrac{3}{5}=\dfrac{3\cdot4}{5\cdot4}=\dfrac{12}{20}\)

mà 5<12

nên \(\dfrac{-14}{-56}< \dfrac{21}{35}\)

z8: \(10A=\dfrac{10^{201}+10}{10^{201}+1}=1+\dfrac{9}{10^{201}+1}\)

\(10B=\dfrac{10^{202}+10}{10^{202}+1}=1+\dfrac{9}{10^{202}+1}\)

\(10^{201}+1< 10^{202}+1\)

=>\(\dfrac{9}{10^{201}+1}>\dfrac{9}{10^{202}+1}\)

=>\(\dfrac{9}{10^{201}+1}+1>\dfrac{9}{10^{202}+1}+1\)

=>10A>10B

=>A>B

D

D

a: =(78+150)/76=238/76=3

b: =5+40=45

c: =1-120/12=1-10=-9

d: =3/2-1/2=1

e: =20+20=40