Now that we have the model built, we can play with the variables to see what effect they have. In the spreadsheet above, go to cell B11, and change the Conversion rate for invites (conv%) to 5%. This will make the Viral Coefficient less than 1. Now look at what that did to your population growth. Instead of continuing to grow, it grows to 20 people, and then stops.
To save time and effort, a person can group two or more of their passive activities into one larger activity, provided they form an "appropriate economic unit." When a taxpayer does this, instead of having to provide material participation in multiple activities, they only have to provide it for the activity as a whole. In addition, if a person includes multiple activities into one group and has to dispose of one of those activities, they’ve only done away with part of a larger activity as opposed to all of a smaller one. 
Speaking of Mad Men during the third season of Mad Men they worked to create buzz through an application called Mad Men Yourself.  The application as an avatar creator that helped you to create an avatar that made a 60s stylized version of yourself.  The site received over half a million visitors the first week.   After five years you can still use the application, and it's going strong.
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Diversify safely but DIVERSITY. You do not need to get the best and highest return all the time. If so, you are not earning passive income you are earning active income which is taxed differently (see IRS.GOV passive -vs- active income definitions). As an investor you do not need to be chasing ‘the almighty dollar’. This is a losing proposition. Make the dollar come to you.
Your income is your greatest wealth-building tool—a tool that typically requires your active participation in the form of a full-time job. You know what I’m talking about! Even if you love your job, I’m willing to bet you wouldn’t mind earning some extra income without the blood, sweat, tears, and time commitment of another job. In fact, there are several benefits. Building a passive income:
In the case of viral marketing, "viral" refers to something that spreads quickly and widely across its audience. Viral marketing is a deliberate enterprise, though the distribution of a message happens organically. As such, social media provides the perfect ecosystem for viral marketing, though it has its roots in traditional word-of-mouth marketing. While the practice was much more widely used in the early to mid-2000s, as new internet businesses were being created in extreme numbers, it is still common among internet-based business-to-consumer (B-to-C) companies. The widespread adoption of social networks, including YouTube, Twitter, Instagram, Snapchat and Facebook, has enabled modern viral marketing efforts and increased their efficacy. 
The reason to make use or virality, the ease in spreading and sharing, is however a double-edged sword. We cannot forget that in this type of campaign, a large part of the control falls into the hands of the users, and we risk the message being misinterpreted or parodied. On the other hand, a successful viral campaign can work miracles for your brand’s results.