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a)\(\left(x+3\right)\times5+1=20\Leftrightarrow5x+15=19\)
\(\Leftrightarrow5x=4\Leftrightarrow x=\frac{4}{5}\)
b)sai đề
c)\(2\frac{3}{7}\times x+1\frac{5}{4}=5\frac{3}{42}\)\(\Leftrightarrow\frac{17}{7}\times x+\frac{9}{4}=\frac{71}{14}\) \(\Leftrightarrow\frac{17}{7}\times x+\frac{63}{28}=\frac{142}{28}\)
\(\Leftrightarrow\frac{17}{7}\times x=\frac{79}{28}\Leftrightarrow x=\frac{17}{7}:\frac{79}{28}\) \(\Leftrightarrow x=\frac{17}{7}\times\frac{28}{79}\Leftrightarrow x=\frac{476}{553}=\frac{68}{79}\)
d)\(10\frac{2}{3}-x:\frac{6}{7}=8\frac{1}{3}-6\frac{2}{7}\Leftrightarrow\frac{32}{3}-x:\frac{6}{7}=\frac{25}{3}-\frac{44}{7}\) \(\Leftrightarrow\frac{224}{21}-x:\frac{6}{7}=\frac{75}{21}-\frac{132}{21}\Leftrightarrow-\frac{57}{21}-\frac{224}{21}\)
\(\Leftrightarrow-x:\frac{6}{7}=-\frac{281}{21}\Leftrightarrow-x=-\frac{281}{21}\times\frac{6}{7}\) \(\Leftrightarrow-x=-\frac{1686}{147}\Leftrightarrow x=\frac{562}{49}=11\frac{23}{49}\)
a) - ta có :1/5=8/40 ; 3/8=15/40
8/40<9/40;10/40;11/40;12/40;13/40;14/40<15/40
\(\Rightarrow\) 6 phân số tối giản lớn hơn 1/5 và nhỏ hơn 3/8 là:9/40;1/4;11/40;3/10;13/40;7/20
b) - ta có: 2/5 =12/30 ; 3/5 = 18/30
12/30<13/30;14/30;15/30;16/30;17/30<18/30
\(\Rightarrow\)5p/số khác nhau nằm giữa 2 p/số 1/5 và 3/8 là: 12/30;13/30;14/30;15/30;16/30;17/30
- ta có: 1 - 5/7 =2/7 1 - 5/6 = 1/6
2/7 =12/42 ; 1/6 = 6/42
12/42>11/42;10/42;9/42;8/42;7/42>6/42
\(\Rightarrow\)5p/số khác nhau nằm giữa 2 p/số 5/7 và 5/6 là: 11/42;10/42;9/42;8/42;7/42
c)
\(1\frac{1}{3}\cdot\frac{1}{8}\cdot1\frac{1}{15}\cdot1\frac{1}{24}\cdot1\frac{1}{35}\)
= 4/3 x 9/8 x 16/15 x 25/24 x 36/35
= (4/3 x 9/8) x (16/15 x 25/24) x 36/35
= 3/2 x 10/9 x 26/35
= (3/2 x 10/9) x 36/35
= 5/3 x 36/35
= 12/7
\(a.\frac{19}{5}\cdot\frac{4}{7}+\frac{3}{7}\cdot\frac{19}{5}-\frac{4}{5}\)
\(=\frac{19}{5}\cdot\left(\frac{4}{7}+\frac{3}{7}\right)-\frac{4}{5}\)
\(=\frac{19}{5}\cdot1-\frac{4}{5}\)
\(=\frac{19}{5}-\frac{4}{5}=\frac{15}{5}=3\)
\(b.2\frac{2}{7}\cdot5\frac{2}{5}+\frac{16}{7}\cdot1\frac{3}{5}+\frac{1}{2}\)
\(=\frac{16}{7}\cdot\frac{27}{5}+\frac{16}{7}\cdot\frac{8}{5}+\frac{1}{2}\)
\(=\frac{16}{7}\cdot\left(\frac{27}{5}+\frac{8}{5}\right)+\frac{1}{2}\)
\(=\frac{16}{7}\cdot7+\frac{1}{2}\)
\(=16+\frac{1}{2}=\frac{33}{2}\)
\(c.\frac{3}{7}\cdot3\frac{3}{4}-\frac{3}{7}\cdot\frac{5}{4}-\frac{1}{4}\)
\(=\frac{3}{7}\cdot\frac{15}{4}-\frac{3}{7}\cdot\frac{5}{4}-\frac{1}{4}\)
\(=\frac{3}{7}\cdot\left(\frac{15}{4}-\frac{5}{4}\right)-\frac{1}{4}\)
\(=\frac{3}{7}\cdot\frac{5}{2}-\frac{1}{4}\)
\(=\frac{15}{14}-\frac{1}{4}=\frac{23}{28}\)
Chú ý: \(\cdot:\times\)
a) \(15-3\left(x-1\right)-x=20\)
\(15-3x+3-x=20\)
\(-4x=2\)
\(x=-\frac{1}{2}\)
b) \(6x-2\left(x+3\right)=10\)
\(6x-2x-6=10\)
\(4x=16\)
\(x=4\)
c) \(25:\left(x+4\right)=5\)
\(x+4=25:5=5\)
\(x=1\)
d tự làm nha!
(y - 2/5) x 1/2 =1
y - 2/5 =1:1/2
y-2/5 = 1x2/1
y-2/5 =2
y =2+2/5
y =2/1 +2/5
y =10/5+2/5
y = 12/5
a) ( 1/2-1/3-1/6).(1/2+2/3+3/4+...+2017/2018) + 3/4.x = 9/10
0.(1/2+2/3+3/4+...+2017/2018) + 3/4.x = 9/10
0+3/4.x = 9/10
3/4.x = 9/10
x = 9/10: 3/4
x = 6/5
b) x + ( 3/1.3+3/3.5+...+3/13.15) = 11/5
x + 3/2. ( 1-1/3 + 1/3 - 1/5 + ...+ 1/13 - 1/15) = 11/5
x + 3/2. ( 1-1/15) = 11/5
x + 3/2.14/15 = 11/5
x + 7/5 = 11/5
x = 11/5 - 7/5
x = 4/5
\(a,x-\frac{5}{6}:1\frac{1}{6}=0,125\)
\(x-\frac{5}{6}:\frac{7}{6}=\frac{1}{8}\)
\(x-\frac{5}{7}=\frac{1}{8}\)
\(x=\frac{1}{8}+\frac{5}{7}\) \(x=\frac{47}{56}\)
\(b,\left(1-\frac{2}{10}+x+\frac{1}{5}\right):\left(1\frac{1}{3}-\frac{2}{3}+3\frac{1}{3}\right)-1=1\frac{1}{2}\)
\(\left(1-\frac{1}{5}+x+\frac{1}{5}\right):\left(\frac{4}{3}-\frac{2}{3}+\frac{10}{3}\right)-1=\frac{3}{2}\)
\(\left(\frac{4}{5}+x+\frac{1}{5}\right):4=\frac{3}{2}+1\)
\(\left(1+x\right):4=\frac{5}{2}\)
\(1+x=\frac{5}{2}.4\)
\(1+x=10\)
\(x=10-1\)
\(x=9\)