DRich
DRich
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November 28th, 2012 at 9:38:58 AM permalink
We are installing a basketball hoop in our warehouse at work and my boss really likes to gamble big. I want to set up a bet with him that he can't make 10 free throws in a row at any point given a maximum of 50 shots.

If I offer him 5 to 1 odds and assume he is a 60% free throw shooter, do I have an advantage and how much? On average what percentage would a free throw shooter have to shoot to have an advantage in this bet?
At my age, a "Life In Prison" sentence is not much of a deterrent.
SOOPOO
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November 28th, 2012 at 11:19:21 AM permalink
Quote: DRich

We are installing a basketball hoop in our warehouse at work and my boss really likes to gamble big. I want to set up a bet with him that he can't make 10 free throws in a row at any point given a maximum of 50 shots.

If I offer him 5 to 1 odds and assume he is a 60% free throw shooter, do I have an advantage and how much? On average what percentage would a free throw shooter have to shoot to have an advantage in this bet?



I think the math would say he could do it 1 in 5 tries or so. But I have to warn you, each free throw is not independent from the previous one. Muscle memory after a successful throw leads to a higher than 60% chance on the next throw. As someone who has hit 60+ free throws in a row, you do get into a 'groove'. On your side might be the choke factor. If the boss has hit 9 in a row, I think different thoughts may enter his mind.
By the way, how do you 'know' he is a 60% foul shooter?
FinsRule
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November 28th, 2012 at 11:31:33 AM permalink
At a summer camp the basketball coach said to us "I will give you $100 if anyone makes 10 3 pointers in a row". We were like 10-11 years old. We had one chance.

My friend went and was the only one to make 10 in a row. Coach said "I don't have $100, here's $1" I'll always hate that guy.
MidwestAP
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November 28th, 2012 at 11:31:45 AM permalink
If he's a 60% free throw shooter (and disregarding the muscle memory aspect, which is a very valid point), he would hit 10 consecutive throws (0.6)^10 which is about 1 in 165 times. He will have 40 tries at it since he has to finish by the 50th throw. So it seems that 5 to 1 works in his favor, 4 to 1 would give you a very slight edge. I'd go for a little more edge like 3 to 1 or 7 to 2.
DRich
DRich
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November 28th, 2012 at 12:19:07 PM permalink
Quote: MidwestAP

If he's a 60% free throw shooter (and disregarding the muscle memory aspect, which is a very valid point), he would hit 10 consecutive throws (.06)^10 which is about 1 in 165 times. He will have 40 tries at it since he has to finish by the 50th throw. So it seems that 5 to 1 works in his favor, 4 to 1 would give you a very slight edge. I'd go for a little more edge like 3 to 1 or 7 to 2.



Your math seems reasonable, but when I simulate it I am only showing the shooter to be successful about 9.8% of the time. I guess I will recheck my simulation.
At my age, a "Life In Prison" sentence is not much of a deterrent.
MidwestAP
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November 28th, 2012 at 12:32:13 PM permalink
Yes, and I should have written the equation as 0.6^10 (not .06), I'll edit my original post.
dwheatley
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November 28th, 2012 at 12:34:22 PM permalink
Quote: DRich

Your math seems reasonable, but when I simulate it I am only showing the shooter to be successful about 9.8% of the time. I guess I will recheck my simulation.



That's because the math is not reasonable. There are a few threads on this site that discuss the calculation of streaks, and despite the good intentions of the poster, this method gives incorrect answers by a large margin.

An online calculator I use gives 9.965% chance of hitting a 60% shot 10 times in a row in 50 trials.
Wisdom is the quality that keeps you out of situations where you would otherwise need it
MangoJ
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November 28th, 2012 at 12:36:21 PM permalink
Quote: MidwestAP

He will have 40 tries at it since he has to finish by the 50th throw.



He doesn't have 40 tries. If he fails at every 10th throw, he only had 5 tries.
dwheatley
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November 28th, 2012 at 12:37:00 PM permalink
Once the shooter has a 64% free throw rate, the odds of hitting the streak increase to 16.8%, which is enough to get an advantage on the bet.
Wisdom is the quality that keeps you out of situations where you would otherwise need it
MidwestAP
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November 28th, 2012 at 12:44:35 PM permalink
Quote: dwheatley

That's because the math is not reasonable. There are a few threads on this site that discuss the calculation of streaks, and despite the good intentions of the poster, this method gives incorrect answers by a large margin.

An online calculator I use gives 9.965% chance of hitting a 60% shot 10 times in a row in 50 trials.



Now that I think about it, I agree that I'm wrong. Each throw has an independent 1 in 165 chance to start a streak of 10 in a row, but that DOES NOT mean that 40 trials at it will give the shooter a little less than a 1 in four chance of hitting 10 in a row. I don't know the calculation, but the simulations seem to be about right.
tringlomane
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November 28th, 2012 at 12:58:13 PM permalink
Yeah as others have said, you don't have 40 chances to succeed, so 0.00983 is correct. The average length of a trial is: 1 + 0.6 + 0.6^2 + 0.6^3 + ... + 0.6^10 = 2.4909300736 shots

To find the probability correctly, you have to write a recursive relation like this in Excel:

=(1-I$1)*G10+(1-I$1)*I$1*G9+(1-I$1)*I$1^2*G8+(1-I$1)*I$1^3*G7+(1-I$1)*I$1^4*G6+(1-I$1)*I$1^5*G5+(1-I$1)*I$1^6*G4+(1-I$1)*I$1^7*G3+(1-I$1)*I$1^8*G2+(1-I$1)*I$1^9*G1+I$1^10

Where I$1 = 0.6 (probability of success)

The wizard discusses this here:

https://wizardofodds.com/ask-the-wizard/probability/coins/

A streak calculator may be found here.

http://www.pulcinientertainment.com/info/Streak-Calculator-enter.html

Giving him 5 to 1 would give you a healthy edge, imo.
DRich
DRich
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November 28th, 2012 at 1:12:21 PM permalink
Thank you everyone, I appreciate the input.

I will offer 5 to 1 which should feed his ego and fatten my bankroll. Hopefully he isn't better than a 64% shooter or else I will be taking the worst of it.
At my age, a "Life In Prison" sentence is not much of a deterrent.
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