2.5 and better. It various, depending on brand and design. The different manufacturers are constantly improving the glide-ratio for their suits.

Lift/Drag x Height loss

To calculate the glide ratio, you divide the length it was thrown, e.g. 150cm, by the height it was thrown, e.g. 50cm. So 150/50=30cm so, it would be 30:1.

That would be a function of the glide ratio of the paper airplane in question.

The 747 has about a 17 to 1 glide ratio. If we figure a cruise altitude of 42,000 ft. (8 miles). Then a 747 in cruise could glide 136 miles. Assuming that the landing area is at sea level. Even if cruise alt is a bit lower, its reasonable to say a large commercial airliner at cruise altitude can glide somewhere around 100 miles.