So going with your sample of $100,000.
1. I have 100 shares 2. Newcomer does $4000 worth of work and therefore gets 4 shares. Meanwhile I have done another $6000 worth of work so I get 6 shares, there are now 106 shares in the company and the company is worth $110,000 (until it can be properly valued based on other metrics).
Just writing this out for myself really, I realise shares issued don't have to be divisible by 100.