Chương III : Phân số

=>3(x-2)=4(x+5)

=>4x+20=3x-6

=>x=-26

\(\dfrac{x-2}{4}=\dfrac{5+x}{3}\\ =>3\times\left(x-2\right)=4\times\left(5+x\right)\\ =>3x-6=20+4x\\ =>3x-4x=20+6\\ =>-x=26\\ =>x=-26\)

`(x-2):4 = (5+x) :3`

`(x-2)*3 = 4*(5+x)`

`3x -6 = 20 +4x`

`3x -4x = 20 +6`

`-x =26`

`x=-26`

=>(2x+3,5)=16/3:8/3=2

=>2x=-1,5

=>x=-0,75

\(\left(3\dfrac{1}{2}+2x\right)\times2\dfrac{2}{3}=5\dfrac{1}{3}\\ =>\left(\dfrac{7}{2}+2x\right)\times\dfrac{8}{3}=\dfrac{16}{3}\\ =>\dfrac{7}{2}+2x=\dfrac{16}{3}:\dfrac{8}{3}\\ =>\dfrac{7}{2}+2x=2\\ =>2x=2-\dfrac{7}{2}\\ =>2x=-\dfrac{3}{2}\\ =>x=-\dfrac{3}{2}:2\\ =>x=-\dfrac{3}{4}\)

\(a,\left(x-\dfrac{1}{2}\right):\dfrac{1}{3}+\dfrac{5}{7}=9\dfrac{5}{7}\)

\(\Leftrightarrow\left(x-\dfrac{1}{2}\right).3=\dfrac{68}{7}-\dfrac{5}{7}\)

\(\Leftrightarrow\left(x-\dfrac{1}{2}\right).3=9\)

\(\Leftrightarrow x-\dfrac{1}{3}=3\)

\(\Leftrightarrow x=3+\dfrac{1}{3}\)

\(\Leftrightarrow x=\dfrac{9}{3}+\dfrac{1}{3}\)

\(\Leftrightarrow x=\dfrac{10}{3}\)

\(b,x+30\%x=-1,31\)

\(\Leftrightarrow x+\dfrac{3}{10}.x=-\dfrac{131}{100}\)

\(\Leftrightarrow x.\left(1+\dfrac{3}{10}\right)=-\dfrac{131}{100}\)

\(\Leftrightarrow x.\dfrac{13}{10}=-\dfrac{131}{100}\)

\(\Leftrightarrow x=-\dfrac{131}{100}.\dfrac{10}{13}\)

\(\Leftrightarrow x=-\dfrac{131}{130}\)

\(c,-\dfrac{2}{3}x+\dfrac{1}{5}=\dfrac{1}{10}\)

\(\Leftrightarrow\dfrac{-2}{3}x=\dfrac{1}{10}-\dfrac{1}{5}\)

\(\Leftrightarrow\dfrac{-2}{3}x=\dfrac{1}{10}-\dfrac{2}{10}\)

\(\Leftrightarrow-\dfrac{2}{3}x=-\dfrac{1}{10}\)

\(\Leftrightarrow x=-\dfrac{1}{10}.\left(-\dfrac{3}{2}\right)\)

\(\Leftrightarrow x=\dfrac{3}{20}\)

a: Giờ 1 đi được 120*1/2=60(km)

Giờ 2 đi được 60*2/5=24(km)

Giờ 3 đi được 60-24=36(km)

b: QUãng đường đi được trong giờ thứ 3 chiếm 36/120=30%

Câu 1:

\(=\dfrac{21}{31}+\dfrac{1}{3}-\dfrac{44}{53}+\dfrac{10}{31}-\dfrac{9}{53}=\dfrac{1}{3}\)

Câu 2:

1: =>1,3x=-1,31

=>130x=-131

=>x=-131/130

2: =>(4,5-2x)=11/14:(-11/7)=-7/14=-1/2=-0,5

=>2x=5

=>x=5/2

Câu 2:

1:=>1,3x=-1,31

=>x=-131/130

2: =>\(\left(4.5-2x\right)=\dfrac{11}{14}:\dfrac{-11}{7}=\dfrac{-1}{2}=-0.5\)

=>2x=5

=>x=5/2

\(11+\dfrac{13}{17}\)

\(=\dfrac{11}{1}+\dfrac{13}{17}\)

\(=\dfrac{187}{17}+\dfrac{13}{17}\)

\(=\dfrac{200}{17}\)

\(=\dfrac{27}{5}\cdot\dfrac{30}{7}+\dfrac{40}{7}\cdot\dfrac{37}{7}=\dfrac{2614}{49}\)

\(c)\)

\(5\dfrac{2}{5}\times4\dfrac{2}{7}+5\dfrac{5}{7}\times5\dfrac{2}{7}\)

\(=\dfrac{27}{5}\times\dfrac{30}{7}+\dfrac{40}{7}\times\dfrac{37}{7}\)

\(=\dfrac{162}{7}+\dfrac{40}{7}\times\dfrac{37}{7}\)

\(=\dfrac{162}{7}+\dfrac{1480}{49}\)

\(=\dfrac{1134}{49}+\dfrac{1480}{49}\)

\(=\dfrac{2614}{49}\)

a: Số học sinh khá là 40*2/5=16 bạn

Số học sinh trung bình là 16:8/11=22 bạn

Số học sinh giỏi là 40-16-22=2 bạn

b: Tỉ số phần trăm giữa số học sinh giỏi so với cả lớp là:

2:40=5%

=>(2x-9/2):3/4=4/3

=>(2x-9/2)=1

=>2x=11/2

=>x=11/4

\(\left(2x-4,5\right):\dfrac{3}{4}-\dfrac{1}{3}=1\)

\(\left(2x-4,5\right):\dfrac{3}{4}=1+\dfrac{1}{3}\)

\(\left(2x-4,5\right):\dfrac{3}{4}=\dfrac{4}{3}\)

\(2x-4,5=\dfrac{4}{3}\times\dfrac{3}{4}\)

\(2x-4,5=1\)

\(2x=1+4,5\)

\(2x=5,5\)

\(x=5,5:2\)

\(x=2,75\)