How many singles do you have to sell to reach the top 40?

Im not sure exactly, this is a question that i would like somebody to answer aswell, but i heard once that between release monday and chart compilement sat/sun, over six days you need to sell in the region of between 400 and 1000 records to get into the top 40.

The top 100 however is a different story. You only need to sell a few to get into the top 100. When i say a few im meaning 10's-100's of copys.

A few sounds crazy easy, but without money for marketing, its hard to sell more than a few in six days.

O' by the way, I think this to be true about Hard Sales rather than internet downloads.