a)=(3/4+3/12)+2/5

=1+2/15

=17/15

b)

(40/17-6/17)+(47/15-4/30)

=2+3=5

k cho minh

Tinh1 bằng cách thuận tiện nhất :

a ) 3/4 + 2/5 + 3/12

= 3/4 + 2/5 + 1/4 

= ( 3/4 + 1/4 ) + 2/5 

= 1 + 2/5 

= 2/5

b ) 47/15 + 40/17 - 4/30 - 6/17

= 47/15 + 40/17 - 2/15 - 6/17

= ( 47/15 - 2/15 ) + ( 40/17 - 6/17 )

= 45/15 + 34 /17

= 3 + 2 

= 5

tk mk nha 

thấy thế nào , comment đi

yêu mọi người nhiều lắm !!!

a)45/60+24/60+15/60=84/60=7/5                                                                                                                                                       b)(47/15-4/30)+(40/17-6/17)=(94/30-4/30)+34/17=90/30+2=3+2=5

Lời giải:

a. $\frac{3}{4}+\frac{2}{5}+\frac{3}{12}=\frac{3}{4}+\frac{2}{5}+\frac{1}{4}$

$=(\frac{3}{4}+\frac{1}{4})+\frac{2}{5}=1+\frac{2}{5}=\frac{7}{5}$

b. $\frac{47}{15}+\frac{40}{17}-\frac{4}{30}-\frac{6}{17}$
$=(\frac{47}{15}-\frac{4}{30})+(\frac{40}{17}-\frac{6}{17})$

$=(\frac{47}{15}-\frac{2}{15})+\frac{34}{17}$

$=\frac{45}{15}+\frac{34}{17}=3+2=5$

a) 3/7 + 4/9 + 4/7 + 5/9

= ( 3/7 + 4/7 ) + ( 4/9 + 5/9 )

= 7/7 + 9/9

= 1  + 1 

= 2

b)1/5 + 4/10 + 9/15 + 16/20 + 25/25 + 36/30 + 49/35 + 64/40 + 81/45

= 1/5 + 2/5 + 3/5 + 4/5 + 5/5 + 6/5 + 7/5 + 8/5 + 9/5

= ( 1/5 + 9/5 ) + ( 2/5 + 8/5 ) + (7/5 + 3/5 ) + ( 4/5 + 6/5  ) + 5/5

= 2 + 2 + 2 + 2 + 1

= 2  x 4 + 1

= 8  +1 

= 9

c)  1/8 + 1/12 + 3/8 + 5/12

= ( 1/8 + 3/8 ) + ( 1/12 + 5/12)

= 4/8 + 6/12

= 1/2 + 1/2

= 2/4 = 1/2

mỏi tay rồi

d; (1 - \(\dfrac{1}{2}\)) x (1 - \(\dfrac{1}{3}\)) x (1 - \(\dfrac{1}{4}\)) x ... x ( 1 - \(\dfrac{1}{100}\))

 = \(\dfrac{1}{2}\) x \(\dfrac{2}{3}\)  x \(\dfrac{3}{4}\) x \(\dfrac{3}{4}\) x ... x \(\dfrac{99}{100}\)

= \(\dfrac{1}{100}\)

e; \(\dfrac{9}{5}\) : \(\dfrac{17}{15}\) + \(\dfrac{8}{5}\) : \(\dfrac{17}{15}\)

=  \(\dfrac{9}{5}\) x \(\dfrac{15}{17}\) + \(\dfrac{8}{5}\) x \(\dfrac{15}{17}\)

=  \(\dfrac{27}{17}\) + \(\dfrac{24}{17}\)

=  \(\dfrac{51}{17}\)

=   3

các bn lm đến đâu cx dc miễn là lm hộ mk cái ạ, ai đang lm vào nhắn tin vs mk để mk bít nha

a; \(-\dfrac{8}{3}+\dfrac{7}{5}-\dfrac{71}{15}< x< -\dfrac{13}{7}+\dfrac{19}{14}-\dfrac{7}{2}\)

              -\(\dfrac{19}{15}\) - \(\dfrac{71}{15}\) < \(x\) < -\(\dfrac{1}{2}\) - \(\dfrac{7}{2}\)

              -6 < \(x\) < -4

             vì \(x\) \(\in\) Z nên \(x\) = -5

- \(\dfrac{19}{6}+\dfrac{-15}{2}+\dfrac{11}{3}\) < \(x\) < - \(\dfrac{5}{4}\) + \(\dfrac{19}{12}\) - \(\dfrac{10}{3}\)

- \(\dfrac{32}{3}+\dfrac{11}{3}< x< \) \(\dfrac{1}{3}\) - \(\dfrac{10}{3}\)

-7 < \(x\) < - 3

Vì \(x\in\) Z nên \(x\in\) {-6;-5;-4}

-8.4+19= -13

-11.3-28=-61

4.(-15)-18=-78

19-4.(-12)=67

-25.(-3)-54=21

-8.4+19=-32+19=-13

-11.3-28=-33-28=-61

4.(-15)-18=-60-18=-78

19-4.(-12)=19-(-48)=67

-25.(-3)-54=75-54=21

-16-7.(-4)+24:(-8)=-16+28-3=12-3=9

15:(-3)+30-7.(-3)=-5+30+21=25+21=46

-48:(-4)+12.(-5)=12-60=-48

-29+65:(-5)+23=-29-13+23=-19

15:(-5)-17-12.(-5)=-3-7+60=-10+60=50

28.(-4)-17=-112-17=-129

-19-7.4=-19-28=-47

-14.(-2)-16=28-16=12

13.(-3)-65-4.(-6)=-39-65+24=-104+24=-80

-24-8.(-6)+28=-24+48+28=24+28=52

phần b là 6+x nha các bạn. mình viết sai đề

= 5 đó bn

tích mk nha!!!!

Bài 1 tính nhanh

A) 21 . 35 - 3 . 25

B)48 . (-21) + (-142) . (-24)

C)77-11 . (30+7)

D)47.(45-15) - 47.(45+15)

Bài 2 tìm x

A) 17-(2+x)=3

B) (^+x) - (17-23) = -11

C)4 .x -15 = -75-x

D) 72-3.x=5.x+8

E)2.(X+1) +3.(x-2)=x-4

                          Dấu chấ