Bài 1:
$a) (75,6-21,7):4+22,82.2\\=53,9:4+45,64\\=13,475+45,64=59,115\\b) 21,56:(75,6-65,8)-0,354:2\\=21,56:9,8-0,177\\=2,2-0,177=2,023$
Bài 2:
$a) x+\frac{1}{5}-2,7=4\frac{1}{2}\\\Leftrightarrow x+\frac{1}{5}-\frac{27}{10}=\frac{9}{2}\\\Leftrightarrow x-\frac{5}{2}=\frac{9}{2}\\\Leftrightarrow x=\frac{9}{2}+\frac{5}{2}=7\\b) 31,5.0,1+x.3=7,65\\\Leftrightarrow 3,15+3x=7,65\\\Leftrightarrow 3x=7,65-3,15=4,5\\\Leftrightarrow x=1,5$
Bài 3:
Gọi số bé, số lớn lần lượt là a,b
Vì số bé thêm 5,66 thì được số lớn$\Rightarrow a+5,66=b$
Ta có: $a+b=8,64\\\Leftrightarrow a+(a+5,66)=8,64\\\Leftrightarrow 2a=2,98\\\Leftrightarrow a=1,49\\\Rightarrow b=a+5,66=1,49+5,66=7,15$
Bài 4:
$a) \frac{3}{7}+\frac{4}{9}:\frac{10}{3}\\=\frac{3}{7}+\frac{4}{9}.\frac{3}{10}\\=\frac{3}{7}+\frac{2}{3}.\frac{1}{5}\\=\frac{3}{7}+\frac{2}{15}=\frac{59}{105}\\b) 4.\frac{12}{17}:\frac{6}{7}\\=4.\frac{12}{17}.\frac{7}{6}\\=4.\frac{2}{17}.7=\frac{56}{17}$
