The ratio in which the yz-plane divides the segment
joining the points (-2, 4, 7) and (3, -5, 8) is

Let yz plane divide the segment joining (-2, 4, 7) and (3, -5, 8) in the ratio $\lambda :1$ .
On yz plane, x-coordinate is zero

$\therefore \frac{3\lambda -2}{\lambda +1}=0\Rightarrow \lambda =\frac{2}{3}$ and the required ratio is 2 : 3.