after i did ios 4.2 update all of apps are not on my ipad were did they go and how do i get them back on ipad

did they sync to your itunes?

if so just re sync them.

if not, you gotta download them one, by one.

Resync should get them back but if you do redownload the AppStore remembers what you have bought so you wouldn't be charged.
Sometimes I've redownloaded apps because I couldn't be bothered to resync.

try resyncing your unit

ok resynching unit several times still no apps how do i redownload apps they show in itunes and when i go to app store on ipad they show in stalled

Ummm, this might be silly, but right after my upgrade all that was on the first page of my iPad was the apple apps that come with it. I stared at it for a minute wondering what had happened to my apps. Then I swiped to bring page two into view, it was blank. Everything was there, but was on pages 3, 4, etc. I had to move them all over. I have no idea why they were rearranged, but since I needed to set up folders it was no big deal. Any chance your apps are simply on some other pages to the right of the one you are looking at?