a, tổng các chữ số a và b là:

27+13=40

vậy a và b là;

40x2=80

số b là:

40;2=20

vậy phân số đó là;

\(\frac{80}{20}\)

đáp số: 80/20

bài 1:

a) \(4\dfrac{1}{2}x:\dfrac{5}{12}=0,5\) ; b)\(1,5+1\dfrac{1}{4}x=\dfrac{2}{3}\)

\(\dfrac{9}{2}x:\dfrac{5}{12}=\dfrac{1}{2}\) \(\dfrac{3}{2}+\dfrac{5}{4}x=\dfrac{2}{3}\)

\(\dfrac{9}{2}x\) \(=\dfrac{1}{2}.\dfrac{5}{12}\) \(\dfrac{5}{4}x=\dfrac{2}{3}-\dfrac{3}{2}\)

\(\dfrac{9}{2}x\) \(=\dfrac{5}{24}\) \(\dfrac{5}{4}x=\dfrac{-5}{6}\)

\(x\) \(=\dfrac{5}{24}:\dfrac{9}{2}\) \(x=\dfrac{-5}{6}:\dfrac{5}{4}\)

\(x\) \(=\dfrac{5}{108}\) \(x=\dfrac{-2}{3}\)

c) Cho mình hỏi x ở đâu vậy ???

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

\(\left(x-5\right)\) \(=\dfrac{2}{5}.\dfrac{1}{3}\) \(\left(\dfrac{9}{2}-2x\right):\dfrac{3}{4}=\dfrac{4}{3}\)

\(x-5\) \(=\dfrac{2}{15}\) \(\dfrac{9}{2}-2x\) =\(\dfrac{4}{3}.\dfrac{3}{4}\)

\(x\) \(=\dfrac{2}{15}+5\) \(\dfrac{9}{2}-2x=1\)

\(x\) \(=\dfrac{77}{15}\) \(2x=\dfrac{9}{2}-1\)

f) \(\left(2,7x-1\dfrac{1}{2}x\right):\dfrac{2}{7}=\dfrac{-21}{7}\) \(2x=\dfrac{7}{2}\)

\(\left(\dfrac{27}{10}x-\dfrac{3}{2}x\right):\dfrac{2}{7}=-3\) \(x=\dfrac{7}{2}:2\)

\(\left[x\left(\dfrac{27}{10}-\dfrac{3}{2}\right)\right]=-3.\dfrac{2}{7}\) \(x=\dfrac{7}{4}\)

\(x.\dfrac{6}{5}=\dfrac{-6}{7}\)

\(x=\dfrac{-6}{7}:\dfrac{6}{5}\)

\(x=\dfrac{-5}{7}\)

bài 2:

Theo bài ra ta có :\(\dfrac{a}{27}=\dfrac{-5}{9}=\dfrac{-45}{b}\)

\(\Rightarrow9a=27.\left(-5\right)\Rightarrow a=\dfrac{27.\left(-5\right)}{9}=-15\)

\(\Rightarrow\left(-5\right)b=\left(-45\right).9\Rightarrow b=\dfrac{\left(-45\right).9}{-5}=81\)

Vậy \(a=-15;b=81\)

tính chất trên gọi là tính chất bắc cầu, ta so sánh hai phân số với một số (phân số) thứ 3.

a) A = 3/7

b) B = 73/13

c) C = 37/7

d) D = 12

ba câu a) ,b) ,c) bn đổi ra hỗn số giúp mk nha

tick cho tớ nha

a) \(A=11\dfrac{3}{13}-\left(3\dfrac{4}{7}-6\dfrac{3}{13}\right)\)

\(=11\dfrac{3}{13}-3\dfrac{4}{7}-6\dfrac{3}{13}\)

\(=\left(11\dfrac{3}{13}-6\dfrac{3}{13}\right)-3\dfrac{4}{7}\)

\(=1\dfrac{3}{7}\)

b) \(B=\left(7\dfrac{4}{9}+3\dfrac{8}{13}\right)-5\dfrac{4}{9}\)

\(=7\dfrac{4}{9}+3\dfrac{8}{13}-5\dfrac{4}{9}\)

\(=\left(7\dfrac{4}{9}-5\dfrac{4}{9}\right)+3\dfrac{8}{13}\)

\(=2+3\dfrac{8}{13}\)

\(=5\dfrac{8}{13}\)

c) \(C=\dfrac{-2}{7}.\dfrac{5}{11}+\dfrac{-2}{7}.\dfrac{6}{11}+5\dfrac{4}{7}\)

\(=\dfrac{-2}{7}.\left(\dfrac{5}{11}+\dfrac{6}{11}\right)+5\dfrac{4}{7}\)

\(=\dfrac{-2}{7}+5\dfrac{4}{7}\)

\(=\dfrac{-5}{7}+\dfrac{12}{7}\)

\(=\dfrac{7}{7}=1\)

d) \(D=0,7.1\dfrac{3}{5}.30.0,375.\dfrac{4}{7}\)

\(=\dfrac{7}{10}.\dfrac{8}{5}.30.\dfrac{375}{1000}.\dfrac{4}{7}\)

\(=\dfrac{36}{5}\)

\(=7,2\)

Ta có \(\dfrac{a}{b}=\dfrac{18}{27}=\dfrac{2}{3}\)

Mà \(ƯCLN\left(a,b\right)=13\)

\(\Rightarrow\dfrac{a}{b}\) sau khi rút gọn cho 13 sẽ bằng \(\dfrac{2}{3}\)

Vậy \(\dfrac{a}{b}=\dfrac{2.13}{3.13}=\dfrac{26}{39}\)

a)\(\dfrac{11}{120};\dfrac{21}{120}\)

b)\(\dfrac{312}{1898};\dfrac{876}{1898}\)

c)\(\dfrac{28}{120};\dfrac{26}{120};\dfrac{-27}{120}\)

d)\(\dfrac{51}{180};\dfrac{-50}{180};\dfrac{-128}{180}\)