Betting On A 7 Game Series

The Warriors are about to play a seven game series vs. the Trail Blazers. In a seven game series, teams continue to play games until one team has won four games. This team is announced the winner of the seven game series.

Being an avid fan, Ted wants to bet $100 that the Warriors will win the series. However, to his dismay, he discovers that he is only able to bet on one game at a time, and can bet up until that game starts.

With a bit of thought, he comes up with a strategy to place his bets for each game (based on results of previous games) so that the final outcome mimics betting on the series, IE he wins $100 if the Warriors win the series and loses $100 if they lose the series.

With this strategy, what is the dollar amount he should bet on the first game? e.g. If he should bet $12.34 on the first game, give your answer as 12.34.

Explicit Example: Consider a three game series, where the team that wins 2 games wins the series. Then, we if bet in the following manner, we see that no matter when the Warriors win (green lines), we get $100, and no matter when Trail Blazers win (pink lines), we get -$100.


This problem was presented to me some time back by my good friend, Matt Cushman.


The answer is 31.25.

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1 solution

Geoff Pilling
May 9, 2016

It is likely easiest to figure out if you work backwards. i.e. Figure out what you would need to bet on whatever games could be the last ones and work backward from there.

Ted's strategy is as follows:

Game Wins Losses Net Bet
Game 1 0 0 $0 $31.25
Game 2 1 0 $31.25 $31.25
0 1 -$31.25 $31.25
Game 3 2 0 $62.50 $25
1 1 $0 $37.50
0 2 -$62.50 $25
Game 4 3 0 $87.50 $12.50
2 1 $37.50 $37.50
1 2 $37.50 $37.50
0 3 -$87.50 $12.50
Game 5 3 1 $75 $25
2 2 $0 $50
1 3 -$75 $25
Game 6 3 2 $50 $50
2 3 -$50 $50
Game 7 3 3 $0 $100

Therefore, the dollar amount he should bet on the first game should be $ 31.25 \boxed{31.25} .

I did not understand the question what's this question all about

Gaurav Chahar - 5 years, 1 month ago

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Its about how to bet on each game of a seven game series to simulate the result of betting $100 on the final outcome. i.e. By betting certain dollar amounts on each game of a seven game series, you want to (a) win $100 at the end if your team wins, and (b) lose $100 at the end if your team loses.

Make sense?

Geoff Pilling - 5 years, 1 month ago

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Anyone else have an idea about how I could more clearly explain the problem?

Geoff Pilling - 5 years, 1 month ago

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@Geoff Pilling Golden State Warriors! Boo yah!

Just for that, I edited the problem. Looks better?


Note: A better way to explain the solution is simply to say "Work backwards".

Calvin Lin Staff - 5 years ago

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@Calvin Lin Looks great, Calvin. Thanks for adding the clarification text and diagram!

Geoff Pilling - 5 years ago

@Calvin Lin And oh yeah, go Warriors!!! 😎😎😎🏀🏀🏀

Geoff Pilling - 5 years ago

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