average chip stack

If there are x people at the start of an mtt and they all start with 1500 chips. How can i found what the average chip count will be when there are x-1 people and x-2 and so on.
Example.
147 players enter. What will average chip count be when there are 29 people left.

I have been trying to figure this out so I can know how long I am able to sit back and watch when i get up early in mtt. I would greatly appreciate any help.

I know this is not a hard equation, but whenever I try I never match what the tourney lobby says.