Step 1: Formula for horizontal range.
The horizontal range \( R \) of a projectile is given by the formula:
\[
R = \frac{v^2 \sin 2\theta}{g}
\]
where \( v \) is the velocity, \( \theta \) is the angle of projection, and \( g \) is the acceleration due to gravity.
Step 2: Comparing ranges.
Since the velocities and the acceleration due to gravity are the same for both cases, the horizontal ranges will be the same because:
\[
\sin 2 \times 30^\circ = \sin 60^\circ \quad \text{and} \quad \sin 2 \times 60^\circ = \sin 120^\circ
\]
Thus, the ratio of the horizontal ranges is \( 1 : 1 \).