Actually, it is. You buy 2 tickets, your odds of winning are now 2:1,000,000, which is 1:500,000. That's why I always buy multiple tickets if I'm playing It would be completely different if you bought one ticket each week for two weeks.

To calculate the risk of flooding, you have to look at the chances of NOT flooding, which is 99%. To go 50 years without a flood is .99^50, or about 60%. That means you have about a 40% chance of a flood in any of those 50 years. I think. It's been a while so my math is fuzzy. If you really want to know probabilites and statistics, the best people to ask aren't statisticans, ask a gambler. They're like human statistic calculators.

Anyway, I think that's drifting away from the original point. One thing that isn't factored into the risk assesment is the severity of the consequences. Two families might both have the same risk of power outages, but if one is in northern Canada in the middle of winter, they have more to worry about than someone living in California.