Photoshop question.

Im having trouble with photoshop resizing my pics pretty low.

for example.

I have a pic taken with my DSLR and its around 8 meg. I edit it in photoshop, then crop it down and save as and it usually drops the MB down to around 2 on high setting.

When i crop, i usually type in 4x6 in the dimensions, but leave the DPI field blank. And i read where it defaults to 300 dpi. Do i need to change this?

 

if the picture is about 8mb, its probably close to a 14megapixel camera. therefore you can print that picture out to about 24x30. so when you resize the picture to 4x6 there is a lot less information that needs to be stored that way it takes up less space.