Resolution is pixel count - 2400x300 pixels for example - and not dpi. It doesn't matter what dpi you set it to - you can change that in PS (or your image editing app of choice).

2400x3000 pixels is the exact same document at 10dpi or 600dpi.

Setting 2400x3000 at 300dpi makes the real world size 8x10 inches for printing for publication (even though most printers only actually print 150 lines per inch - and you can set it to 150dpi for printing on your inkjet printer, or through a photo lab, and it becomes a 16x20 in real world dimensions).

This is why many publications tell you the pixel count they desire and don't even mention the dpi setting for you to choose. You can change that "setting" in post (as it affects nothing).

-Lew ;-)