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a) 2/5 x 1/6 x 1/9 =1/5x1/9=1/45
b) 2/5 x 1/6 : 1/9 = 1/5x9=9/5
c)2/5 : 1/6 x 1/9 =2/5x6x1/9=12/5x1/9=12/45

57 \(\times\) 46 + 57 \(\times\) 54
= 57 \(\times\) ( 46 + 54)
= 57 \(\times\) 100
= 5700
137 + 355 + 63 + 45
= ( 137 + 63) + ( 355 + 45)
= 200 + 400
= 600
215 \(\times\) 48 - 215 \(\times\) 38
= 215 \(\times\) ( 48 - 38)
= 215 \(\times\) 10
= 2150
4 \(\times\) 50 \(\times\) 25
= ( 4 \(\times\) 25) \(\times\) 50
= 100 \(\times\) 50
= 5 000
57×(46+54) =57×100=5700
137+355+63+45=(137+63) +(355+45) =200+400=600
215×48-215×38=215×(48-38) =215×10=2150
4×50×25=(4×25) ×50=100×50=5000

\(a)\frac{3}{5}\times\frac{2}{5}+\frac{3}{4}\times\frac{3}{5}\)
\(=\frac{3}{5}\times\left(\frac{2}{5}+\frac{3}{4}\right)\)
\(=\frac{3}{5}\times\left(\frac{8}{20}+\frac{15}{20}\right)\)
\(=\frac{3}{5}\times\frac{23}{20}\)
\(=\frac{69}{100}\)
\(b)\frac{5}{9}\times\frac{7}{3}\times\frac{9}{5}\)
\(=\left(\frac{5}{9}\times\frac{9}{5}\right)\times\frac{7}{3}\)
\(=1\times\frac{7}{3}\)
\(=\frac{7}{3}\)

\(\dfrac{9}{10}\times2+3\times\dfrac{9}{10}+\dfrac{9}{10}:\dfrac{1}{5}\)
\(=\dfrac{9}{10}\times2+\dfrac{9}{10}\times3+\dfrac{9}{10}\times5\)
\(=\dfrac{9}{10}\times\left(2+3+5\right)\)
\(=\dfrac{9}{10}\times10\)
\(=\dfrac{90}{10}\)
\(=9\)


\(\dfrac{14}{9}\) x \(\dfrac{11}{8}-\dfrac{3}{8}\) x \(\dfrac{14}{9}\)
\(=\dfrac{14}{9}\) x \(\left(\dfrac{11}{8}-\dfrac{3}{8}\right)\)
\(=\dfrac{14}{9}\) x \(\dfrac{8}{8}=\dfrac{14}{9}\) x \(1\)
\(=\dfrac{14}{9}\)

(a x 27 + 116 x b): c
= (1368 x 27 + 116 x 54) : 108
= (36936 + 6264) : 108
= 43200 : 108
= 400
( a x 27 + 116 x b ) : c
= ( 1368 x 27 + 116 x 54 ) : 108
= ( 684 x 54 + 116 x 54 ) : 108
= [ ( 684 + 116 ) x 54 ] : 108
= ( 800 x 54 ) : 108
= 400 x 108 : 108
= 400

a,Ta có \(\frac{x}{6}=\frac{2}{3}\)
\(\Rightarrow3x=12\Rightarrow x=4\)
Vậy x = 4
b, \(\left(\frac{4}{7}+\frac{8}{9}\right)-\frac{5}{9}=\frac{4}{7}+\frac{8}{9}-\frac{5}{9}\)
\(=\frac{4}{7}+\left(\frac{8}{9}-\frac{5}{9}\right)\)
\(=\frac{4}{7}+\frac{1}{3}\)
\(=\frac{19}{21}\)
Bài 1 mình nhầm. x phần 6 = 4 phần 7 mới đúng. Cảm ơn bạn nhé
46 x 9 + 54 x 9
= 9 x (46 + 54)
= 9 x 100
= 900
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