Say you have 100,000 DAUs and a retention rate of 80%, and for every five users, one of them tells a friend each day to download your app (and they do it). You get 20k new users per day just from word of mouth. In this equation, Xn is the number of DAUs today and Xn+1 is the number of DAUs tomorrow:
X n+1 = (X n * 80%) + (X n * (1⁄5))
If you start w...
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