![image](https://tex.z-dn.net/?f=%5Cfrac%7Ba%7D%7Bb%7D%3D+%5Cfrac%7B5%7D%7B3%7D+%3D+%3E+3a+%3D+5b+%3D%3E+a+%3D+%5Cfrac%7B5b%7D%7B3%7D+%3B%5C%5C%0A%5Cfrac%7B3a%7D%7B10b%7D%3D%5Cfrac%7B3%5Ccdot+%5Cfrac%7B5b%7D%7B3%7D%7D%7B10b%7D%3D%5Cfrac%7B3%5Ccdot5b%7D%7B3%5Ccdot10b%7D%3D%5Cfrac%7B1%7D%7B2%7D.)
3a = 5b => a = \frac{5b}{3} ;\\
\frac{3a}{10b}=\frac{3\cdot \frac{5b}{3}}{10b}=\frac{3\cdot5b}{3\cdot10b}=\frac{1}{2}." alt="\frac{a}{b}= \frac{5}{3} = > 3a = 5b => a = \frac{5b}{3} ;\\
\frac{3a}{10b}=\frac{3\cdot \frac{5b}{3}}{10b}=\frac{3\cdot5b}{3\cdot10b}=\frac{1}{2}." align="absmiddle" class="latex-formula">
Ответ: а) 1:2.