4-level commission of language exchange website
www.chinesegreat.com/CG/F.jsp?c=313
If you invite 10 friends to be our members and each consumes 100 credits on it
And they each also invite 10 friends respectively and so forth.
You get:
100×5%×10+100×2%×100+100×1%×1000+100×1%×10000=11250Credits