If you were to line up all the planets in our solar system end-to-end, what would be the approximate combined diameter?
The diameters of the eight planets in our solar system are as follows (approximate values):

Mercury: 4,880 km
Venus: 12,104 km
Earth: 12,742 km
Mars: 6,779 km
Jupiter: 139,822 km
Saturn: 116,460 km
Uranus: 50,724 km
Neptune: 49,244 km

To find the combined diameter, we simply add up the individual diameters:

Combined diameter = Mercury + Venus + Earth + Mars + Jupiter + Saturn + Uranus + Neptune
                              = 4,880 km + 12,104 km + 12,742 km + 6,779 km + 139,822 km + 116,460 km + 50,724 km + 49,244 km
                              ≈ 392,755 km

So, if you were to line up all the planets in our solar system end-to-end, their approximate combined diameter would be 392,755 kilometers.