[Skulemate]

Umm... well, your math is fine, though sometimes we rely on calculators too much... you need exactly four 1/4" ID tubes to make one 1/2" ID tube (pi is a constant... so the only thing that changes is r^2... and since the radius is doubled from 1/4 to 1/2, the area is four times larger). However, there'd likely be a fair bit of flow resistance in the manifold, especially if you were splitting the 1/2" tube into the four 1/4" ones.