giup minh voi mn oi

A=  \(\frac{221}{210}\)

k tui nha, hậu tạ

sao mày o làm nhanh ả

\(a.=\left(\dfrac{4}{5}.\dfrac{5}{6}\right).\dfrac{2}{3}=\dfrac{4}{6}.\dfrac{2}{3}=\dfrac{4}{9}\)

\(b.\dfrac{4}{5}.\dfrac{3}{4}+\dfrac{5}{4}.\dfrac{3}{4}=\dfrac{3}{5}+\dfrac{15}{16}=\dfrac{123}{80}\)

\(c.\left(\dfrac{11}{23}+\dfrac{9}{23}\right)+\left(\dfrac{2}{23}+\dfrac{18}{23}\right)=\dfrac{20}{23}+\dfrac{20}{23}=\dfrac{40}{23}\)

\(d.\left(\dfrac{27}{12}-\dfrac{25}{36}\right)+\left(\dfrac{17}{6}-\dfrac{15}{6}\right)=\dfrac{14}{9}+\dfrac{1}{3}=\dfrac{17}{9}\)

dấu chấm là gì vậy

Giải:

A=5/9+2/15-6/9

   =(5/9-6/9)+2/15

   = -1/9 + 2/15

   = 1/45

B=2/7-3/8+4/7+1/7-5/8+5/15

   = (2/7+4/7+1/7) + (-3/8-5/8) +1/3

   = 1+ (-1) +1/3

   =1/3

C=3/5+1/15+1/57+1/3-2/9-3/4-1/36

   =9/15+1/15+1/57+19/57-8/36-27/36-1/36

   =(9/15+1/15)+(1/57+19/57)+(-8/36-27/36-1/36)

   =2/3+20/57+(-1)

   =58/57+(-1)

   =1/57

D=1/1.2+1/2.3+1/3.4+...+1/99.100

   =1/1-1/2+1/2-1/3+1/3-1/4+...+1/99-1/100

   =1/1-1/100

   =99/100

Câu E mình ko biết làm nhé!

3 \(\times\) \(\dfrac{4}{15}\) + 2 \(\times\) \(\dfrac{4}{15}\) - 5 \(\times\) \(\dfrac{4}{15}\)

= \(\dfrac{4}{15}\) \(\times\) ( 3 + 2 - 5)

= \(\dfrac{4}{15}\) \(\times\) 0

= 0

0 nha

1.x=4

2.x=6

3.x=8

Bài 1:

a: \(\frac{5\times7}{15}=\frac{35}{15}=\frac73\)

b: \(8:\frac{16}{23}=8\times\frac{23}{16}=\frac{8}{16}\times23=23\times\frac12=\frac{23}{2}\)

c: \(\frac{8}{15}:5=\frac{8}{15\times5}=\frac{8}{75}\)

d: \(\frac{15}{19}\times3=\frac{15\times3}{19}=\frac{45}{19}\)

Bài 2:

a: \(3\times\frac49+\frac23-\frac{7}{18}\)

\(=\frac43+\frac23-\frac{7}{18}\)

\(=\frac63-\frac{7}{18}=2-\frac{7}{18}=\frac{36}{18}-\frac{7}{18}=\frac{29}{18}\)

b: \(\frac{7}{10}\times\frac23-\frac14=\frac{14}{30}-\frac14=\frac{28}{60}-\frac{15}{60}=\frac{28-15}{60}=\frac{13}{60}\)

c: \(\frac98-\frac78:\frac56=\frac98-\frac78\times\frac65\)

\(=\frac98-\frac{42}{40}=\frac{45}{40}-\frac{42}{40}=\frac{3}{40}\)

d: \(\frac23+\frac12:\frac32-\frac{11}{24}\)

\(=\frac23+\frac12\times\frac23-\frac{11}{24}\)

\(=\frac23+\frac13-\frac{11}{24}=1-\frac{11}{24}=\frac{13}{24}\)

Bài 3:

Độ dài đáy tương ứng với chiều cao là: \(\frac35\times2=\frac65\left(m\right)\)

Chu vi hình bình hành là:

\(\left(\frac65+\frac45\right)\times2=\frac{10}{5}\times2=2\times2=4\left(m\right)\)

Diện tích bình hành là;

\(\frac65\times\frac35=\frac{18}{25}\left(m^2\right)\)

Cho tổng trên là A

Ta co : 

\(A=\frac{9}{1.2}+\frac{9}{2.3}+\frac{9}{3.4}+...+\frac{9}{98.99}+\frac{9}{99.100}\)

\(A=9\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{98.99}+\frac{1}{99.100}\right)\)

\(A=9\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\)

\(A=9\left(\frac{1}{1}-\frac{1}{100}\right)\)

\(A=9.\frac{99}{100}\)

\(A=\frac{891}{100}\)