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November 14th, 2011, 11:19 AM   #1
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probability dice

If you roll two fair dice, one red and one green. Whatis the probability that you get a sum of 7 given that one die is an even number?
Thank you.
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November 14th, 2011, 11:41 AM   #2
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Re: probability dice

6 possibilities for 7 with 1 die even

1 + 6
6 + 1
4 + 3
3 + 4
5 + 2
2 + 4

possibilities with at least 1 die even = 3*3+3*3+3*3 = 27

answer: 6/27
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November 14th, 2011, 11:54 AM   #3
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Re: probability dice

sorry, I dont get it
why possibilities with at least 1 die even = 3*3+3*3+3*3 = 27?
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November 14th, 2011, 12:07 PM   #4
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Re: probability dice

Quote:
Originally Posted by mathproblems
sorry, I dont get it
why possibilities with at least 1 die even = 3*3+3*3+3*3 = 27?
first die even, second die uneven: 3*3
second die even, first die uneven: 3*3
first die even, second die even: 3*3
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November 14th, 2011, 12:12 PM   #5
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Re: probability dice

sorry, can did you get 3?
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November 14th, 2011, 12:30 PM   #6
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Re: probability dice

Quote:
Originally Posted by mathproblems
sorry, can did you get 3?
because there are 3 even and 3 uneven values on a die
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November 15th, 2011, 06:58 AM   #7
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Re: probability dice

Hello, mathproblems!

Quote:
You roll two fair dice, one red and one green.
What is the probability that you get a sum of 7, given that one die is an even number?







1,\,6),\2,\,5),\3,\,4),\4,\,3),\5,\,2) ,\6,\,1)" />



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November 15th, 2011, 07:38 AM   #8
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Re: probability dice

If you are given that one die is even, it means that precisely one die is even right? Meaning the other is odd.
18 possibilities to have precisely 1 even. So a 1/3 chance that it'll give a 7.
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November 15th, 2011, 07:40 AM   #9
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Re: probability dice

thank you. sounds great
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November 16th, 2011, 10:08 PM   #10
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Re: probability dice

Specific Multiplication Rule

Only valid for independent events

P(A and B) = P(A) * P(B)
Example 3:

P(A) = 0.20, P(B) = 0.70, A and B are independent.
B B' Marginal
A 0.14 0.06 0.20
A' 0.56 0.24 0.80
Marginal 0.70 0.30 1.00
The 0.14 is because the probability of A and B is the probability of A times the probability of B or 0.20 * 0.70 = 0.14.

Dependent Events

If the occurrence of one event does affect the probability of the other occurring, then the events are dependent.

Conditional Probability

The probability of event B occurring that event A has already occurred is read "the probability of B given A" and is written: P(B|A)

General Multiplication Rule

Always works.

P(A and B) = P(A) * P(B|A)
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