A body of mass $m_1$ moving with a velocity $10\;ms^{-1}$ collides with another body at rest of mass $m_2$. After collision the velocities of the two bodies are $2\;ms^{-1}$ and $5 \; ms^{-1}$ respectively, along the direction of motion of $m_1$. The ratio $\frac{m_1}{m_2}$ is :
