Rolling 5 Dice: Probability of At Least 3 Sixes

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Discussion Overview

The discussion revolves around calculating the probability of rolling at least 3 sixes when five standard 6-sided dice are rolled. Participants explore different methods of counting successful outcomes and express confusion over initial calculations.

Discussion Character

  • Mathematical reasoning, Debate/contested

Main Points Raised

  • One participant calculates the total outcomes as 7776 and initially finds 360 successful outcomes, leading to a probability of 360/7776.
  • Another participant points out that the first calculation is incorrect due to double-counting the scenarios where four or five sixes occur, suggesting a different counting method that involves calculating the exact number of ways to achieve three, four, and five sixes separately.
  • A third participant acknowledges the correction with a brief expression of gratitude.
  • A fourth participant proposes using the complement rule to calculate the probability, presenting a formula that results in a different probability of 23/648.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct probability calculation, with multiple competing methods and results presented.

Contextual Notes

Some calculations depend on the correct interpretation of counting successful outcomes, and there are unresolved issues regarding the application of the complement rule versus direct counting methods.

Who May Find This Useful

Individuals interested in probability theory, combinatorics, or those seeking to understand different approaches to solving probability problems involving dice.

veronica1999
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Five standard 6-sided dice are rolled. What is the probability that at least 3 of them show a six?

I am surprised my answer is wrong.

First the total outcomes are 6x6x6x6x6=7776

Successful outcomes 10x6x6=360
There are 10 ways to choose 3 from 5 and then the remaining 2 can be any number.

360/7776 is not the answer.

The answer is 276/7776.:confused:
 
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Re: dice problem

veronica1999 said:
Five standard 6-sided dice are rolled. What is the probability that at least 3 of them show a six?

I am surprised my answer is wrong.

First the total outcomes are 6x6x6x6x6=7776

Successful outcomes 10x6x6=360
There are 10 ways to choose 3 from 5 and then the remaining 2 can be any number.

360/7776 is not the answer.

The answer is 276/7776.:confused:
You have double-counted the ways in which four or five sixes can occur. What you should do is to count the number of ways in which exactly three sixes can occur (10x5x5), then add the number of ways in which four sixes can occur (5x5), and finally the one way in which five sixes can occur.
 
Re: dice problem

Oops...
Thanks!:D
 
Re: dice problem

I would use the complements rule:

$$P(X)=1-\frac{{5 \choose 0}5^5+{5 \choose 1}5^4+{5 \choose 2}5^3}{6^5}=\frac{23}{648}$$
 

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