Ta có: 85 x a = 34 x 125 (nhân chéo)

           85a = 4250

                a = 4250 : 85

                a = 50

Vậy a= 50 thì \(\frac{a}{125}\text{=}\frac{34}{85}\)

a=50 nha bạn

a=125.34/85=50 ^^

\(\frac{a}{125}=\frac{2}{5}\)=> a = 125 : 5 x 2 = 50

Vậy a = 50

\(a=\frac{125.34}{85}=50\)

Vậy a=50

Ta có : \(\frac{34}{85}=\frac{2}{5}\)

Để : \(\frac{a}{125}=\frac{2}{5}\)thì \(a=125:5\cdot2=50\)

Vậy : Để   \(\frac{a}{125}=\frac{34}{85}\)thì \(a=50\)

ko biết

tính 3A rồi => A = 34/49 

tính 3B => B = 26/49 

=> A/B = 17/13

\(A=\frac{34}{7.13}+\frac{51}{13.22}+\frac{85}{22.37}+\frac{68}{37.49}\)

\(=17.\left(\frac{2}{7.13}+\frac{3}{13.22}+\frac{5}{22.37}+\frac{4}{37.49}\right)\)

\(=\frac{17}{3}.\left(\frac{6}{7.13}+\frac{9}{13.22}+\frac{15}{22.37}+\frac{12}{37.49}\right)\)

\(=\frac{17}{3}\left(\frac{1}{7}-\frac{1}{13}+\frac{1}{13}-\frac{1}{22}+\frac{1}{22}-\frac{1}{37}+\frac{1}{37}-\frac{1}{49}\right)\)

\(=\frac{17}{3}\left(\frac{1}{7}-\frac{1}{49}\right)\)

\(B=\frac{39}{7.16}+\frac{65}{16.31}+\frac{52}{31.43}+\frac{26}{43.49}\)

\(=13\left(\frac{3}{7.16}+\frac{5}{16.31}+\frac{4}{31.43}+\frac{2}{43.49}\right)\)

\(=\frac{13}{3}\left(\frac{9}{7.16}+\frac{15}{16.31}+\frac{12}{31.43}+\frac{6}{43.49}\right)\)

\(=\frac{13}{3}\left(\frac{1}{7}-\frac{1}{16}+\frac{1}{16}-\frac{1}{31}+\frac{1}{31}-\frac{1}{43}+\frac{1}{43}-\frac{1}{49}\right)\)

\(=\frac{13}{3}\left(\frac{1}{7}-\frac{1}{49}\right)\)

\(\Rightarrow\frac{A}{B}=\frac{\frac{17}{3}\left(\frac{1}{7}-\frac{1}{49}\right)}{\frac{13}{3}\left(\frac{1}{7}-\frac{1}{49}\right)}=\frac{\frac{17}{3}}{\frac{13}{3}}=\frac{17}{13}\)