a: \(\dfrac{1}{15}+\dfrac{7}{15}-\dfrac{2}{15}=\dfrac{1+7-2}{15}=\dfrac{6}{15}=\dfrac{2}{5}\)
b: \(\dfrac{14}{21}\cdot\dfrac{5}{8}+\dfrac{5}{8}\cdot\dfrac{13}{21}+\dfrac{6}{8}\cdot\dfrac{-5}{21}\)
\(=\dfrac{5}{8}\cdot\dfrac{14}{21}+\dfrac{5}{8}\cdot\dfrac{13}{21}-\dfrac{5}{8}\cdot\dfrac{6}{21}\)
\(=\dfrac{5}{8}\left(\dfrac{14}{21}+\dfrac{13}{21}-\dfrac{6}{21}\right)=\dfrac{5}{8}\cdot\dfrac{21}{21}=\dfrac{5}{8}\)
c: \(\dfrac{1}{4}+\dfrac{3}{4}\left(\dfrac{2}{3}-\dfrac{1}{2}\right)+\dfrac{6}{16}\)
\(=\dfrac{1}{4}+\dfrac{3}{8}+\dfrac{4-3}{6}\cdot\dfrac{3}{4}\)
\(=\dfrac{5}{8}+\dfrac{1}{6}\cdot\dfrac{3}{4}=\dfrac{5}{8}+\dfrac{1}{8}=\dfrac{6}{8}=\dfrac{3}{4}\)
d: \(x-\dfrac{2}{3}=\dfrac{5^2}{21}:\dfrac{5}{7}\)
=>\(x-\dfrac{2}{3}=\dfrac{25}{21}\cdot\dfrac{7}{5}=\dfrac{5}{3}\)
=>\(x=\dfrac{5}{3}+\dfrac{2}{3}=\dfrac{7}{3}\)
e: \(\dfrac{54}{19}\cdot x+\dfrac{16}{5}=\dfrac{1}{2}\)
=>\(x\cdot\dfrac{54}{19}=\dfrac{1}{2}-\dfrac{16}{5}=\dfrac{-27}{10}\)
=>\(x=-\dfrac{27}{10}:\dfrac{54}{19}=-\dfrac{27}{10}\cdot\dfrac{19}{54}=\dfrac{-19}{20}\)
a) 1/15 + 7/15 - 2/15
= 6/15
= 2/5
b) 14/21 . 5/8 + 5/8 . 13/21 + 6/8 . (-5/21)
= 5/8 . (14/21 + 13/21 - 6/21)
= 5/8 . 1
= 5/8
c) x - 2/3 = 5²/21 : 5/7
x - 2/3 = 25/21 . 7/5
x - 2/3 = 5/3
x = 5/3 + 2/3
x = 7/3
d) 54/19 x + 16/5 = 1/2
54/19 x = 1/2 - 16/5
54/19 x = -27/10
x = -27/10 : 54/19
x = -19/20
a: 1421⋅58+58⋅1321+68⋅−5211421⋅58+58⋅1321+68⋅−521
=58(1421+1321−621)=58⋅2121=58=58(1421+1321−621)=58⋅2121=58
c: =14+38+4−36⋅34=14+38+4−36⋅34
x−23=5221:57�−23=5221:57
=>x=53+23=73�=53+23=73
e: x⋅5419=12−165=−2710�⋅5419=12−165=−2710
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