20\(x\) - 16 = 44
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Ta có: \(-\frac{72}{45}=\frac{-72:9}{45:9}=\frac{-8}{5}\)

a) Ta có: \(\dfrac{x}{y}=\dfrac{20}{9}\Rightarrow\dfrac{x}{20}=\dfrac{y}{9}\)
Áp dụng tính chất dãy tỉ số bằng nhau ta có:
\(\dfrac{x}{20}=\dfrac{y}{9}=\dfrac{x-y}{20-9}=\dfrac{-44}{11}=-4\)
\(\Rightarrow\left\{{}\begin{matrix}x=20\cdot-4=-80\\y=-4\cdot9=-36\end{matrix}\right.\)
b) \(\dfrac{x}{y}=2\dfrac{1}{2}\Rightarrow\dfrac{x}{y}=\dfrac{5}{2}\Rightarrow\dfrac{x}{5}=\dfrac{y}{2}\)
Áp dụng tính chất dãy tỉ số bằng nhau ta có:
\(\dfrac{x}{5}=\dfrac{y}{2}\Rightarrow\dfrac{x+y}{5+2}=\dfrac{40}{7}\)
\(\Rightarrow\left\{{}\begin{matrix}\text{x}=\dfrac{40}{7}\cdot5=\dfrac{200}{7}\\y=\dfrac{40}{7}\cdot2=\dfrac{80}{7}\end{matrix}\right.\)

s) 6450 + 6540 + 550 - 540
= ( 6450 + 550 ) + ( 6540 - 540 )
= 7000 + 6000
= 13000
b) 25 x 20 x 4 x 5 x 7
= ( 25 x 4 ) x ( 20 x 5 ) x 7
= 100 x 100 x 7
= 10000 x 7
= 70000
c) 44 + 44 x 16 + 44 x 2 - 44 x 9
= 44 x 1 + 44 x 16 + 44 x 2 - 44 x 9
= 44 x ( 1 + 16 + 2 - 9 )
= 44 x 10
= 440
a)
\(6450+6540+550-540\)
\(=\left(6450+550\right)+\left(6540-540\right)\)
\(=7000+6000\)
\(=13000\)
b)
\(25\times20\times4\times5\times7\)
\(=\left(25\times4\right)\times\left(20\times5\right)\times7\)
\(=100\times100\times7\)
\(=10000\times7\)
\(=70000\)
c)
\(44+44\times16+44\times2-44\times9\)
\(=44\times1+44\times16+44\times2-44\times9\)
\(=44\times\left(1+16+2-9\right)\)
\(=44\times10\)
\(=440\)

44-40+36-32+28-24+20-16+12-8+4-0=4+4+4+4+4+4=4x6=24

\(\dfrac{7}{16}+\dfrac{-1}{8}+\dfrac{9}{32}=\dfrac{14}{32}-\dfrac{4}{32}+\dfrac{9}{32}=\dfrac{19}{32}\)
\(\dfrac{5}{4}-\dfrac{25}{30}\times\dfrac{37}{44}+\dfrac{-25}{30}\times\dfrac{13}{44}+\dfrac{-25}{30}\times\dfrac{-6}{44}\)
\(=-\dfrac{25}{30}\times\left(\dfrac{5}{4}+\dfrac{37}{44}+\dfrac{13}{44}-\dfrac{6}{44}\right)\)
\(=-\dfrac{25}{30}\times\left(\dfrac{55}{44}+\dfrac{37}{44}+\dfrac{13}{44}-\dfrac{6}{44}\right)\)
\(=-\dfrac{25}{30}\times\dfrac{99}{44}\)
\(=-\dfrac{5}{6}\times\dfrac{9}{4}\)
\(=-\dfrac{15}{8}\)
\(\left(\dfrac{7}{16}+\dfrac{-1}{8}+\dfrac{9}{32}\right):\dfrac{5}{4}\)
\(=\left(\dfrac{14}{32}+\dfrac{-4}{32}+\dfrac{9}{32}\right):\dfrac{5}{4}\)
\(=\dfrac{19}{32}:\dfrac{5}{4}\)
\(=\dfrac{19}{32}.\dfrac{4}{5}=\dfrac{19.4}{32.5}=\dfrac{19}{40}\)
\(\dfrac{-25}{30}.\dfrac{37}{44}+\dfrac{-25}{30}.\dfrac{13}{44}+\dfrac{-25}{30}.\dfrac{-6}{44}\)
\(=\dfrac{-25}{30}.\left(\dfrac{37}{44}+\dfrac{13}{44}+\dfrac{-6}{44}\right)\)
\(=\dfrac{-25}{30}.\dfrac{44}{44}=\dfrac{-5}{6}.1=-\dfrac{5}{6}\)

a) (44 x 52 x 60) : (11 x 13 x 15)
= (44 : 11) x ( 52 : 13) x (60 : 15)
= 4 x 4 x 4 = 64
d) 1 + 6 + 11 + 16 + ... + 46 + 51
Ta có : 1 + 6 + 11 + 16 + ... + 46 + 51 ( có 11 số )
= (51 + 1) x 11 : 2 = 286
\(x - 16 = 44\)
Lời giải:
\(20 x - 16 = 44\)
\(20 x = 44 + 16\)
\(20 x = 60\)
\(x = \frac{60}{20} = 3\)
Đáp số:
\(\boxed{x = 3}\)
20x - 16 =44
20x = 44 +16
20x = 60
x = 60 : 20
x = 3