Suppose that you've just heard of scandal and you're the first one to know. You pass it on to four person in matter of 30 minutes. Each of these four in turn passes it to four other persons in the next 30 minutes and so on.
How long it will take for everybody in the World to get to know scandal?
Suppose that nobody hears it more than once and the population of the World is approximately 5.6 billions.