X + 10% x X + 20% x X +30% x X = 4,8
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Số tiền Mai tiết kiệm trong 1 ngày là:
\(20000-12000-5000=3000\left(đồng\right)\)
Số tiền Mai tiết kiệm sau 15 ngày là \(3000\cdot15=45000\left(đồng\right)\)
=>Chọn B
![](https://rs.olm.vn/images/avt/0.png?1311)
42x(13+78)+9x(87+22)x5
= 42 x 92 + 9 x 109 x 5
= 3864 + 981 x 5
= 3864 + 4905
= 8769
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a: \(\left(-25,5\right):5=\dfrac{-25,5}{5}=-5,1\)
b: \(1\dfrac{3}{2}-0,25+\dfrac{10}{9}\cdot\dfrac{3}{5}\)
\(=\dfrac{5}{2}-0,25+\dfrac{30}{45}\)
\(=\dfrac{5}{2}-\dfrac{1}{4}+\dfrac{2}{3}=\dfrac{9}{4}+\dfrac{2}{3}=\dfrac{27}{12}+\dfrac{8}{12}=\dfrac{35}{12}\)
\(a,\left(-25,5\right):5\)
\(=\left(-5,1\right)\)
\(b,1\dfrac{3}{2}-0,25+\dfrac{10}{9}.\dfrac{3}{5}\)
\(=\dfrac{5}{2}-\dfrac{1}{4}+\dfrac{10}{9}.\dfrac{3}{5}\)
\(=\dfrac{5}{2}-\dfrac{1}{4}+\dfrac{2}{3}\)
\(=\dfrac{10}{4}-\dfrac{1}{4}+\dfrac{2}{3}\)
\(=\dfrac{9}{4}+\dfrac{2}{3}\)
\(=\dfrac{35}{12}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(\dfrac{-3}{7}+\dfrac{4}{21}=\dfrac{-3\cdot3}{21}+\dfrac{4}{21}=\dfrac{-9}{21}+\dfrac{4}{21}=\dfrac{-9+4}{21}=-\dfrac{5}{21}\)
b) \(\left(-0,346\right)+\left(-1,2\right)=-1,546\)
a: \(\dfrac{-3}{7}+\dfrac{4}{21}=-\dfrac{9}{21}+\dfrac{4}{21}=-\dfrac{5}{21}\)
b: \(\left(-0,346\right)+\left(-1,2\right)=-\left(1,2+0,346\right)=-1,546\)
a) Làm tròn số thập phân 1,2756 đến hàng đơn vị.
b)Tìm x biết \(\dfrac{x-2}{7}\) = \(\dfrac{6}{21}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(1,2756\simeq1\)
b: \(\dfrac{x-2}{7}=\dfrac{6}{21}\)
=>\(\dfrac{x-2}{7}=\dfrac{2}{7}\)
=>x-2=2
=>x=2+2=4
a) 1,2756 ≃ 1
b)
\(\dfrac{x-2}{7}=\dfrac{6}{21}\\ =>x-2=\dfrac{6}{21}\cdot7=\dfrac{6}{3}=2\\ =>x=2+2=4\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{3}{5}:1,5+20\%-3\dfrac{1}{4}\)
\(=\dfrac{3}{5}:\dfrac{3}{2}+\dfrac{1}{5}-\dfrac{13}{4}\)
\(=\dfrac{2}{5}+\dfrac{1}{5}-\dfrac{13}{4}=\dfrac{3}{5}-\dfrac{13}{4}=\dfrac{12}{20}-\dfrac{65}{20}=\dfrac{-53}{20}\)
\(\dfrac{3}{5}:1,5+20\%-3\dfrac{1}{4}\\ =\dfrac{3}{5}:\dfrac{3}{2}+\dfrac{1}{5}-\dfrac{13}{4}\\ =\dfrac{3}{5}\cdot\dfrac{2}{3}+\dfrac{1}{5}-\dfrac{13}{4}\\ =\dfrac{2}{5}+\dfrac{1}{5}-\dfrac{13}{4}\\ =\dfrac{3}{5}-\dfrac{13}{4}\\ =\dfrac{12}{20}-\dfrac{65}{20}\\ =\dfrac{-53}{20}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a.8,2+\left(-3,5\right)+50+3,5+\left(-8,2\right)\\ =\left(8,2-8,2\right)+\left(3,5-3,5\right)+50\\ =0+0+50\\ =50\\ b.\dfrac{8}{15}\cdot\dfrac{-45}{4}\\ =\dfrac{4\cdot2}{15}\cdot\dfrac{15\cdot-3}{4}\\ =2\cdot-3\\ =-6\)
a: \(8,2+\left(-3,5\right)+50+3,5+\left(-8,2\right)\)
\(=\left(8,2-8,2\right)+\left(3,5-3,5\right)+50\)
=0+0+50
=50
b: \(\dfrac{8}{15}\cdot\dfrac{-45}{4}=\dfrac{8}{4}\cdot\dfrac{-45}{15}=2\cdot\left(-3\right)=-6\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: x:1,25=-2,4
=>\(x=-2,4\cdot1,25=-3\)
b: \(\dfrac{5}{8}x-\dfrac{7}{24}=-\dfrac{2}{3}\)
=>\(\dfrac{5}{8}x=-\dfrac{2}{3}+\dfrac{7}{24}=-\dfrac{16}{24}+\dfrac{7}{24}=-\dfrac{9}{24}=-\dfrac{3}{8}\)
=>\(x=-\dfrac{3}{8}:\dfrac{5}{8}=-\dfrac{3}{8}\cdot\dfrac{8}{5}=-\dfrac{3}{5}\)
giải giúp mình đang cần
\(x+10\%\cdot x+20\%\cdot x+30\%\cdot x=4,8\)
=>\(x\left(1+0,1+0,2+0,3\right)=4,8\)
=>\(x\cdot1,6=4,8\)
=>\(x=4.8:1.6=3\)