Let the two circles have centers $O_1$ and $O_2$ with radii 5 cm and 3 cm, respectively.
The distance between their centers is:
$ O_1O_2 = 5 + 3 = 8 \text{ cm} $
Let $T$ be the external point where the direct common tangent meets the line joining the centers externally in the ratio $k:1$. The ratio is given by:
$ \frac{O_1T}{O_2T} = \frac{r_1}{r_2} = \frac{5}{3} $
Thus, the ratio in which the direct common tangent divides the line joining the centers externally is:
$ \boxed{5:3} $
Here is the solution :