In general the expectation of making X is given by \int x dP(x). In simpler terms suppose you have a 9% chance of making $1000 a 1% chance of making $10k

In general the expectation of making X is given by \int x dP(x). In simpler terms suppose you have a 9% chance of making $1000 a 1% chance of making $10k and a 90% chance of making $100, your expectation is .09*1000+.01*10000+.9*100 == 280 In you article you only take into account a fraction of the total probability that is equivalent to assuming that in the vast majority of cases you'll make exactly zero. That would mean lowering the previous estimate to $190.