x :8 = 21
x/4 + x/8 + x : 2 = 21/8
\(\dfrac{x}{4}+\dfrac{x}{8}+x:2=\dfrac{21}{8}\\ x\times\left(\dfrac{1}{8}+\dfrac{1}{4}+\dfrac{1}{2}\right)=\dfrac{21}{8}\\ x\times\dfrac{7}{8}=\dfrac{21}{8}\\ x=3.\)
\(\dfrac{x}{4}\) + \(\dfrac{x}{8}\) + \(\dfrac{x}{2}\) = \(\dfrac{21}{8}\)
\(x\) \(\times\) ( \(\dfrac{1}{4}\) + \(\dfrac{1}{8}\) + \(\dfrac{1}{2}\)) = \(\dfrac{21}{8}\)
\(x\) \(\times\) \(\dfrac{7}{8}\) = \(\dfrac{21}{8}\)
\(x\) = \(\dfrac{21}{8}\) : \(\dfrac{7}{8}\)
\(x\) = 3
\(\dfrac{x}{4}+\dfrac{x}{8}+\dfrac{x}{2}=\dfrac{21}{8}\)
\(\left(\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{2}\right).x=\dfrac{21}{8}\)
\(\left(\dfrac{2}{8}+\dfrac{1}{8}+\dfrac{4}{8}\right).x=\dfrac{21}{8}\)
\(\dfrac{7}{8}.x=\dfrac{21}{8}\)
\(x=\dfrac{21}{8}:\dfrac{7}{8}\)
\(x=\dfrac{21}{8}.\dfrac{8}{7}=3\)
Tính nhanh : 9/15 x 5/21 + 29/21 x 2/5 + 9/5 x 8/21
các bạn làm đủ bước nhé.
tìm các sô nguyên x biêt
5/21+-3/7<x/21+8/21
(x+21) chia hết cho 7;(x+21) chia hết cho 8;(x+21) chia hết cho 9 và 200<x<500
6/16:3/6 < x < 20/21 : 4/21
8/21 x 7 /2 < x < 11/8 x 4
a: =>3/8x6/3<x<20/21x21/4
=>3/4<x<5
hay \(x\in\left\{1;2;3;4\right\}\)
b: =>56/42<x<11/2
=>4/3<x<11/2
nên \(x\in\left\{2;3;4;5\right\}\)
6/16:3/6 < x < 20/21 : 4/21
8/21 x 7 /2 < x < 11/8 x 4
a: =>3/8x6/3<x<20/21x21/4
=>3/4<x<5
hay \(x\in\left\{1;2;3;4\right\}\)
b: =>56/42<x<11/2
=>4/3<x<11/2
nên \(x\in\left\{2;3;4;5\right\}\)
a) ( 21/22 + 3/5 + -21/22 ) : 1 2/5 9/17 x 8/5 - 9/17 x 3/5 + 8/17
X - 3/10 = 7/15 x 3/15
a: \(=\dfrac{3}{5}:\dfrac{7}{5}=\dfrac{3}{5}\cdot\dfrac{5}{7}=\dfrac{3}{7}\)
b: \(=\dfrac{9}{17}\left(\dfrac{8}{5}-\dfrac{3}{5}\right)+\dfrac{8}{17}\)
=9/17+8/17=1
c: =>x-3/10=7/15*1/5=7/75
=>x=7/75+3/10=59/150
tìm số nguyên x,y,z ;
a) 6/5 = 18/x
b) 3/4 = -21/x
c) x/4 = 21/28
d) -8/2x = 3/-9
e) -4/11 = x/22 = 40/z
f) - 3/4 = x/20 = 21 / y
g) -4/8 = x/-10 = -7/y = z/-24
h) x/4 = 9/x
\(a.\dfrac{6}{5}=\dfrac{18}{x}\Rightarrow x=\dfrac{18\cdot5}{6}=15\\ \text{Vậy}\text{ }x=15.\)
\(b.\dfrac{3}{4}=\dfrac{-21}{x}\Rightarrow x=\dfrac{-21\cdot4}{3}=28\\ \text{ }\text{ }\text{ }\text{ }\text{Vậy }x=28.\)
\(c.\dfrac{x}{4}=\dfrac{21}{28}\Rightarrow x=\dfrac{21\cdot4}{28}=3\\ \text{Vậy }x=3.\)
\(d.\dfrac{-8}{2x}=\dfrac{3}{-9}\Rightarrow x=\dfrac{-8\cdot\left(-9\right)}{3}:2=12\\ \text{Vậy }x=12.\)
\(e.\dfrac{-4}{11}=\dfrac{x}{22}=\dfrac{40}{z}\\ \Rightarrow x=\dfrac{-4\cdot22}{11}=-8\\ \Rightarrow z=\dfrac{22\cdot40}{-8}=-110\\ \text{Vậy }x=-8;z=-110.\)
\(f.\dfrac{-3}{4}=\dfrac{x}{20}=\dfrac{21}{y}\\ \Rightarrow x=\dfrac{-3\cdot20}{4}=-15\\ \Rightarrow y=\dfrac{21\cdot20}{-15}=-28\\ \text{Vậy }x=-15;y=-28.\)
\(g.\dfrac{-4}{8}=\dfrac{x}{-10}=\dfrac{-7}{y}=\dfrac{z}{-24}\\ \Rightarrow x=\dfrac{-4\cdot\left(-10\right)}{8}=5\\ \Rightarrow y=\dfrac{-7\cdot\left(-10\right)}{5}=14\\ \Rightarrow z=\dfrac{-7\cdot\left(-24\right)}{14}=12\\ \text{Vậy }x=5;y=14;z=12.\)
\(h.\dfrac{x}{4}=\dfrac{9}{x}\\ \Rightarrow x\cdot x=9\cdot4\\ \Rightarrow x\cdot x=36\\ \Rightarrow x\cdot x=6\cdot6\\ \text{Vậy }\text{cả hai }x=6.\)
a) \(\dfrac{-11}{15}< \dfrac{x}{15}< \dfrac{-8}{15}\)
b) \(\dfrac{3}{7}< \dfrac{x}{21}< \dfrac{2}{3}\)
c) \(\dfrac{-67}{21}< \dfrac{x}{168}< \dfrac{-3}{8}\)
a) Ta có: \(\dfrac{-11}{15}< \dfrac{x}{15}< \dfrac{-8}{15}\)
nên -11<x<-8
hay \(x\in\left\{-10;-9\right\}\)
b) Ta có: \(\dfrac{3}{7}< \dfrac{x}{21}< \dfrac{2}{3}\)
\(\Leftrightarrow\dfrac{9}{21}< \dfrac{x}{21}< \dfrac{14}{21}\)
Suy ra: 9<x<14
hay \(x\in\left\{10;11;12;13\right\}\)
c) Ta có: \(\dfrac{-67}{21}< \dfrac{x}{168}< \dfrac{-3}{8}\)
nên \(\dfrac{-536}{168}< \dfrac{x}{168}< \dfrac{-63}{168}\)
Suy ra: -536<x<-63
hay \(x\in\left\{-535;-534;...;-64\right\}\)
Tính theo mẫu :
Mẫu : 13/21 + 5/7 = 13/21 + 5 x 3 / 7 x 3 = 13/21 + 15/21 = 28/21
26/81 + 4/27
5/64 + 7/8
\(\dfrac{26}{81}+\dfrac{4}{27}=\dfrac{26+12}{81}=\dfrac{38}{81}\)
\(\dfrac{5}{64}+\dfrac{7}{8}=\dfrac{5+56}{64}=\dfrac{61}{64}\)
\(\dfrac{26}{81}+\dfrac{4}{27}=\dfrac{26}{81}+\dfrac{4\times3}{27\times3}=\dfrac{26}{81}+\dfrac{12}{81}=\dfrac{38}{81}\)
\(\dfrac{5}{64}+\dfrac{7}{8}=\dfrac{5}{64}+\dfrac{7\times8}{8\times8}=\dfrac{5}{64}+\dfrac{56}{64}=\dfrac{61}{64}\)