Theorem on Equal Ratios

If $\dfrac{a_1}{b_1}=\dfrac{a_2}{b_2}=\dfrac{a_3}{b_3}=\dots =\dfrac{a_n}{b_n}$ then, each ratio equals $\dfrac{m_1a_1+m_2a_2+m_3a_3+\dots + m_na_n}{m_1b_1+m_2b_2+m_3b_3+\dots + m_nb_n}$ for some constants $m_i$ .