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25 tháng 10 2017

\(\dfrac{a}{3}\)=\(\dfrac{b-3}{4}\)=\(\dfrac{c+5}{15}\)

=>\(\dfrac{a}{3}\)=\(\dfrac{b-3+3}{4+3}\)=\(\dfrac{c+5-15}{15-5}\)

=>\(\dfrac{a}{3}\)=\(\dfrac{b}{7}\)=\(\dfrac{c}{10}\)

Áp dụng tính chất dãy tỉ số bằng nhau và a+b+c=34 có:

\(\dfrac{a}{3}\)=\(\dfrac{b}{7}\)=\(\dfrac{c}{10}\)=>\(\dfrac{a+b+c}{3+7+10}\)=\(\dfrac{34}{20}\)=1,7

Với \(\dfrac{a}{3}\)=1,7 => a=1,7 x 3 = 5,1

Với \(\dfrac{b}{7}\)=1.7 => b= 1,7 x 7 =11.9

Với\(\dfrac{c}{10}\)=1,7=> c= 1,7 x 10 = 17

KL:Vậy a=5,1 ; b=11,9 ; c=17

a: \(A=\dfrac{19}{9}+\dfrac{4}{11}+\dfrac{2}{3}=\dfrac{209}{99}+\dfrac{44}{99}+\dfrac{66}{99}=\dfrac{319}{99}\)

b: \(B=\dfrac{-50}{60}+\dfrac{-35}{60}+\dfrac{12}{60}=\dfrac{-73}{60}\)

c: \(C=\dfrac{-27}{36}+\dfrac{132}{36}+\dfrac{10}{36}=\dfrac{115}{36}\)

d: \(D=\dfrac{-19}{3}+\dfrac{2}{3}-\dfrac{4}{5}=\dfrac{-17}{3}-\dfrac{4}{5}=\dfrac{-85-12}{15}=-\dfrac{97}{15}\)

a) Ta có: \(a\left(-\dfrac{3}{2}\right)+a\cdot\dfrac{1}{4}-a\cdot\dfrac{5}{6}\)

\(=a\left(-\dfrac{3}{2}+\dfrac{1}{4}-\dfrac{5}{6}\right)\)

\(=a\left(\dfrac{-18}{12}+\dfrac{3}{12}-\dfrac{10}{12}\right)\)

\(=a\cdot\dfrac{-25}{12}\)(1)

Thay \(a=\dfrac{3}{5}\) vào biểu thức (1), ta được:

\(\dfrac{3}{5}\cdot\dfrac{-25}{12}=\dfrac{-75}{60}=\dfrac{-5}{4}\)

19 tháng 3 2021

a) Ta có: a(−32)+a⋅14−a⋅56

=a(−32+14−56)

=a(−1812+312−1012)

=a⋅−2512(1)

Thay a=35 vào biểu thức (1), ta được:

9 tháng 5 2022

B1 :

a) \(\dfrac{2}{15}+3=\dfrac{2}{15}+\dfrac{15}{5}=\dfrac{17}{5}\)

b) \(2-\dfrac{7}{4}=\dfrac{8}{4}-\dfrac{7}{4}=\dfrac{1}{4}\)

c) \(\dfrac{17}{6}-\dfrac{11}{12}\times6=\dfrac{17}{6}-\dfrac{11}{2}=-\dfrac{8}{3}\)

d) \(\dfrac{14}{17}:7-\dfrac{15}{34}=\dfrac{2}{17}-\dfrac{5}{34}=\dfrac{4}{34}-\dfrac{5}{34}=-\dfrac{1}{34}\)

B3 :

\(x:23=146\)

\(x=146\times23\)

\(x=3358\)

b) \(x\times38=4066\)

\(x=4066:38\)

\(x=107\)

c) \(787+x\times67=2658\)

\(x\times67=2658-787\)

\(x\times67=1871\)

\(x=1871:67\)

\(x=\dfrac{1871}{67}\)

9 tháng 5 2022

từng bài thôi 

12 tháng 11 2021

1.
a)10/7
b) 1
c) 3
d) 3/4
e) -1
2.
a)-3/8
b)x= 3 và x=-2
c)x=10 và x=-20

12 tháng 11 2021

Cảm ơn bạn ! ^^

9 tháng 11 2018

a.\(\dfrac{17}{15}\div\dfrac{4}{3}=\dfrac{17}{20}\)

b.\(\dfrac{-12}{21}\div\dfrac{34}{43}=\dfrac{-86}{119}\)

c.\(\dfrac{-5}{9}\times\dfrac{3}{11}+\dfrac{13}{18}\times\dfrac{3}{11}\)

=\(\dfrac{3}{11}\times(\dfrac{-5}{9}+\dfrac{13}{18})=\dfrac{3}{11}\times\dfrac{1}{6}=\dfrac{1}{22}\)

d.\(\dfrac{-2}{9}\times\dfrac{5}{11}+\dfrac{-16}{9}\times\dfrac{5}{11}=\dfrac{5}{11}\times(\dfrac{-2}{9}+\dfrac{-16}{9})\)

=\(\dfrac{5}{11}\times(-2)=\dfrac{-10}{11}\)

23 tháng 3 2022

\(c,\dfrac{-3}{8}.\dfrac{2}{5}+\dfrac{-3}{8}.\dfrac{14}{5}\\ =\dfrac{-3}{8}.\left(\dfrac{2}{5}+\dfrac{14}{5}\right)\\ =\dfrac{-3}{8}.\dfrac{16}{5}\\ =\dfrac{-6}{5}\\ d,\left(\dfrac{1}{4}+\dfrac{11}{9}\right):\dfrac{34}{5}+\left(\dfrac{-2}{9}+\dfrac{29}{4}\right):\dfrac{34}{5}\\ =\left(\dfrac{1}{4}+\dfrac{11}{9}\right).\dfrac{5}{34}+\left(\dfrac{-2}{9}+\dfrac{29}{4}\right).\dfrac{5}{34}\\ =\left(\dfrac{1}{4}+\dfrac{11}{9}+\dfrac{-2}{9}+\dfrac{29}{4}\right).\dfrac{5}{34}\\ =\left[\left(\dfrac{1}{4}+\dfrac{29}{4}\right)+\left(\dfrac{11}{9}+\dfrac{-2}{9}\right)\right].\dfrac{5}{34}\\ =\left(\dfrac{15}{2}+1\right).\dfrac{5}{34}\\ =\dfrac{17}{2}.\dfrac{5}{34}\\ =\dfrac{5}{4}\)

23 tháng 3 2022

c) \(\dfrac{-3}{8}.\dfrac{2}{5}+\dfrac{-3}{8}.\dfrac{14}{5}\)

\(=\dfrac{-3}{8}.\left(\dfrac{2}{5}+\dfrac{14}{5}\right)\)

\(=\dfrac{-3}{8}.\dfrac{16}{5}\)

\(=\dfrac{-6}{5}\)

Giải thích rút gọn 16 cho 8 được 2

1 tháng 7 2021

\(a,5x\dfrac{7}{3}=\dfrac{5}{1}x\dfrac{7}{3}=\dfrac{35}{3};b,\dfrac{13}{4}:7=\dfrac{13}{4} :\dfrac{7}{1}=\dfrac{13}{4}x\dfrac{1}{7}=\dfrac{13}{28}\)

1 tháng 7 2021

1. Tính 

\(a,5\times\dfrac{7}{3}=\dfrac{35}{3}\)

\(b,\dfrac{13}{4}:7=\dfrac{13}{4}\times\dfrac{1}{7}=\dfrac{13}{28}\)

2. Tính

\(a,\dfrac{3}{7}+\dfrac{2}{5}+\dfrac{3}{4}\)

\(=\dfrac{15}{35}+\dfrac{14}{35}+\dfrac{3}{4}\)

\(=\dfrac{29}{35}+\dfrac{3}{4}\)

\(=\dfrac{116}{140}+\dfrac{105}{140}\)

\(=\dfrac{221}{140}\)

\(b,\dfrac{9}{7}-\dfrac{5}{11}\times\dfrac{11}{7}\)

\(=\dfrac{9}{7}-\dfrac{55}{77}\)

\(=\dfrac{99}{77}-\dfrac{55}{77}\)

\(=\dfrac{44}{77}=\dfrac{4}{7}\)

\(c,\dfrac{3}{5}\times\dfrac{5}{7}+\dfrac{4}{7}\)

\(=\dfrac{3}{5}\times\left(\dfrac{5}{7}+\dfrac{4}{7}\right)\)

\(=\dfrac{3}{5}\times\dfrac{9}{7}\)

\(=\dfrac{27}{35}\)

\(d,\dfrac{7}{9}\times\dfrac{2}{5}:\dfrac{3}{11}\)

\(=\dfrac{14}{45}:\dfrac{3}{11}\)

\(=\dfrac{14}{45}\times\dfrac{11}{3}\)

\(=\dfrac{154}{135}\)

\(e,\dfrac{9}{7}+\dfrac{2}{3}-\dfrac{1}{4}\)

\(=\dfrac{27}{21}+\dfrac{14}{21}-\dfrac{1}{4}\)

\(=\dfrac{41}{21}-\dfrac{1}{4}\)

\(=\dfrac{164}{84}-\dfrac{21}{84}\)

\(=\dfrac{143}{84}\)

\(g,\dfrac{4}{9}:\dfrac{3}{5}\times\dfrac{2}{11}\)

\(=\dfrac{4}{9}\times\dfrac{5}{3}\times\dfrac{2}{11}\)

\(=\dfrac{20}{27}\times\dfrac{2}{11}\)

\(=\dfrac{40}{297}\)

\(h,\dfrac{7}{2}-\dfrac{3}{10}:\dfrac{2}{5}\)

\(=\left(\dfrac{7}{2}-\dfrac{3}{10}\right):\dfrac{2}{5}\)

\(=\left(\dfrac{35}{10}-\dfrac{3}{10}\right):\dfrac{2}{5}\)

\(=\dfrac{32}{10}:\dfrac{2}{5}\)

\(=\dfrac{16}{5}\times\dfrac{5}{2}\)

\(=\dfrac{80}{10}=8\)

a) \(\dfrac{3}{5}+\dfrac{11}{20}=\dfrac{12}{20}+\dfrac{11}{20}=\dfrac{23}{20}\)

b) \(\dfrac{5}{8}-\dfrac{4}{9}=\dfrac{45}{72}-\dfrac{32}{72}=\dfrac{13}{72}\)

c) \(\dfrac{9}{16}\times\dfrac{4}{3}=\dfrac{3}{4}\)

d) \(\dfrac{4}{7}:\dfrac{8}{11}=\dfrac{4}{7}\times\dfrac{11}{8}=\dfrac{11}{14}\)

e) \(\dfrac{3}{5}+\dfrac{4}{5}:\dfrac{2}{5}=\dfrac{3}{5}+\dfrac{4}{5}\times\dfrac{5}{2}=\dfrac{3}{5}+2=\dfrac{3}{5}+\dfrac{10}{5}=\dfrac{13}{5}\)

1 tháng 4 2022

a, 23/20

b, 13/72

c, 3/4

d,11/14

e, 13/5