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Comment by X6S1x6Okd1st | Hacker News Reader

Of course there's always the chance that there are multiple winners which affects either it's expected positive roi

That is in the article, which mentions there's a 50% chance you're going to share the prize.

So let's do the math. 35 cents go to non-jackpot prizes, so the ROI on that is 35 cents, leaving 1.65 for the jackpot. ROI on the jackpot is $1B / 400M odds. That's $2.50 shared amongst the winners. 50% of that is single winner, 50% is shared so $1.25 + $1.25 / 2 = $1.875. $1.875 is greater than 1.65, so the ROI for this lottery is slightly positive. (I don't have the numbers on odds of 3 or more sharing, so the ROI is actually slightly less than $1.875, but it won't be much of a reduction).

Article also said only 75 cents go to the jackpot. the rest goes to the government

The jackpot accumulates. It grew so high because there are many weeks worth of 75 cents. It's an average. Most weeks 0 cents goes to the jackpot because nobody wins, so on the weeks somebody wins, it's often significantly more than 75 cents.

This is obvious because they're selling $400 million worth of tickets to a $1B jackpot.

> The jackpot accumulates. It grew so high because there are many weeks worth of 75 cents. It's an average. Most weeks 0 cents goes to the jackpot because nobody wins, so on the weeks somebody wins, it's often significantly more than 75 cents.

This sentence does not compute. If nobody wins for a week then however many tickets that were sold times 75 cents get added to the jackpot. If somebody wins, the jackpot is reset to $0.

> This is obvious because they're selling $400 million worth of tickets to a $1B jackpot.

$400M this week? Because they should have sold about 1.33 billion $2 tickets without a winner to reach a $1B jackpot, however many weeks that takes.

But I'm not buying tickets on the weeks with low jackpots, just the weeks with billion dollar ones.

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