Bài 1:suy ra 5*(44-x)=3*(x-12)

                 220-5x=3x-36

                 -5x-3x=-36-220

                 -8x      =-256

                   x=32

Bài 2 :Đặt a/3=b/4=k

   suy ra a=3k ; b=4k

Ta có a*b=48

suy ra 3k*4k=48

         12k =48

         k=4

suy ra a=3*4=12

         b=4*4 =16 

Bài 3: áp dụng tính chất dãy số bằng nhau ta được 

    a+b+c+d/3+5+7+9 = 12/24=0,5

suy ra a=1,5;   b=2,5;    c=3,5;          d=4,

phiền quá đi

ko làm dc ak?

\(a,\frac{a}{12}=\frac{b}{9}=\frac{c}{5}\)

Đặt \(\frac{a}{12}=\frac{b}{9}=\frac{c}{5}=k\Rightarrow\hept{\begin{cases}a=12k\\b=9k\\c=5k\end{cases}}\)

Ta có \(abc=12k\cdot9k\cdot5k=20\)

\(\Rightarrow540k^3=20\)

\(\Rightarrow k^3=\frac{20}{540}=\frac{1}{27}\)

\(\Rightarrow k=\frac{1}{3}\)

Với \(k=\frac{1}{3}\Rightarrow\hept{\begin{cases}a=\frac{1}{3}\cdot12=4\\b=\frac{1}{3}\cdot9=3\\c=5\cdot\frac{1}{3}=\frac{5}{3}\end{cases}}\)

a) Đặt \(\frac{a}{12}=\frac{b}{9}=\frac{c}{5}=k\)

\(\rightarrow a=12k,b=9k,c=5k\)

Ta có: \(abc=20\)

\(\rightarrow12k\cdot9k\cdot5k=20\)

\(\rightarrow540\cdot k^3=20\rightarrow k^3=\frac{1}{27}\)

\(\rightarrow k^3=\left(\frac{1}{3}\right)^3\rightarrow k=\frac{1}{3}\)

\(a=12k\rightarrow a=12\cdot\frac{1}{3}=4\)

\(b=9k\rightarrow b=9\cdot\frac{1}{3}=3\)

\(c=5k\rightarrow c=5\cdot\frac{1}{3}=\frac{5}{3}\)

Vậy \(a=4,b=3,c=\frac{5}{3}\)

a=120

b=50

c=90

bạn thử lại nhé!

I don't now

or no I don't

..................

sorry

a) ta có:\(\frac{a}{b}=\frac{5}{8}\Rightarrow8a=5b\)

ab=360\(\Rightarrow5ab=1800\Rightarrow8a^2=1800\Rightarrow225=a^2\Rightarrow a=15\)

đề câu b hình như sai bạn ạ

sao đang 5ab=1800 lại thành 8amũ2=1800 vậy nhỉ

b)-5/12 . 2/11+(-5/12) . 9/11+5/12

=(-5/12+5/12).(2/11+9/11)

=0.1=0

c)6/9/10+(2/5-1/10)

=69/10+3/10

=36/5

\(b)\)\(\frac{-5}{12}.\frac{2}{11}+\frac{-5}{12}.\frac{9}{11}+\frac{5}{12}\)

\(=\frac{-5}{12}.\frac{2}{11}+\frac{-5}{12}.\frac{9}{11}+\frac{5}{12}.1\)

\(=\frac{-5}{12}.\left(\frac{2}{11}+\frac{9}{11}+1\right)\)

\(=\frac{-5}{12}.2\)

\(=\frac{-5}{6}\)

\(c)\)\(6\frac{9}{10}+\left(\frac{2}{5}-\frac{1}{10}\right)\)

\(=6\frac{9}{10}+\frac{2}{5}-\frac{1}{10}\)

\(=\left(6\frac{9}{10}-\frac{1}{10}\right)+\frac{2}{5}\)

\(=6\frac{4}{5}+\frac{2}{5}\)

\(=6\frac{6}{5}=7\frac{1}{5}\)